On Who Wants to Be a Millionaire, Regis Philbin's famous catchphrase was "Is that your final answer?" You should keep the same thing in mind when buying stuff, because spending a few seconds to check could save you a substantial stash of moolah.

Not counting "used" (B-stock and refurbished) goods and store cards, here are 5 modifiers which affect the final price of what you buy, whether it's in person or on the Internet:

1. Coupons & promo codes

How easy! Surely you've heard of these — magical slips of paper that give you a spontaneous discount at the register. Or online, it's even easier (and saves trees): just paste the code into the order form at checkout.

Offline, there's no shortage of flyers being mailed to the point where it becomes overwhelming. If you don't already have a few favorite stores, focus on your options and weigh not just individual item coupons, but the overall shopping experience. (It doesn't make sense to save a few cents and be let down by unhelpful staff.) Find out if you can be apprised of specials online, since they tend to be more searchable. For example, Costco has paper coupon booklets, but they (and many Costcoholics, apparently) also post them on the web, which makes them easier to find or even setup an automatic alert for. This includes big things you're waiting for the price to drop on — such as an HDTV or fridge.

Clipping paper coupons is a time-honored art which my Mom excelled at, the details of which are beyond this article's scope. But one principle which must always be stated is: most coupons for lower-priced goods (like food) don't make much of a difference in isolation. It's in aggregate that the savings add up. However, while you can make more money, you can never make more time, so consider whether the laborious task of scouring booklets and compiling your coupons — a crimp on convenience — is worth the cost. This is highly individual and needs to meet your needs, as some people enjoy coupon-clipping as a hobby. Don't knock 'em!

Online, RetailMeNot is essential. It's user-powered, meaning many people submit promo codes and other people vote on their accuracy. Stale/expired coupons sink into the red while hot ones rise upwards. Some vendors feel threatened by this collective knowledge so they've asked RetailMeNot to exclude them, but other companies actively participate in promos. Be skeptical, however, as they may make something look better than it actually is. That's marketing for ya.

Always look out for stackable coupons. Some deals mavens have mastered combining them, such as:

  • a time-unlimited $50 off +
  • a one-week special which removes a further $25 +
  • extra 10% off if you buy 2.

The math can get confusing, but don't let that deter you from savings, because web checkout forms usually assist with calculations.

2. Cashback

Cashback often comes in the form of: you need to sign up, then click on a special link which tracks you when you buy something. Then, after an elapsed amount of time (so the participating company can reap a net profit), you get your cash back (literally). Under this are all manner of economic and social complexities, such as partner sites receiving commission payments.

Cashback tends to be smaller amounts like 2-10% and there are many flavors — FatWallet is one of the more popular sites to have strategically turned cashbacking into a community — but there are occasional jackpots. For instance, eBay's Buy It Now thru Microsoft Live Search once rose as high as 35% (!), and while I missed out on that, the cashback amount was at a still-respectable 25% when I opted for some pricey music gear. I ended up saving myself over $600 (it took a rolling 60 days to receive all my money after the orders had taken place).

One downside of cashback programs, including the eBay-Microsoft one: at-face prices may be inflated slightly or hugely, so be careful the cashback doesn't merely reduce the price to its usual parity.

Like coupons, take advantage of compound savings whenever possible: there've been a few times where I didn't just stack coupons, there was also cashback, sweetening the deal further. And sometimes there are rebates on top of that.

3. Rebates

Rebates come in different flavors, but they all have one thing in common: motivating you to take action (buy!) when you might normally not be so interested.

MIR stands for Mail-In Rebate, another way of enticing you to buy an item with a lower final cost, but you need to wait weeks, or even months to get a check in the mail as compensation. If money is tight today, be sure to factor that in. The waiting game can be tense and rebate programs often have strict rules, such as how your claim form is filled out, and what you need to include from the original packaging — commonly both a copy of the receipt and original UPC (bar code). Let me assure you, it sucks to go through that trouble, miss out one detail, and receive a rejection letter instead of money. Some rebate programs are shady and unresponsive, so search for others who've dealt with certain companies before.

This is why I prefer instant rebates — just like a coupon, but even easier, because it's automatically applied at checkout. All you have to do is buy. Ah, consumerism.

4. Shipping

Don't be fooled by "free shipping". It sounds tasty but often isn't true, as the cost is eaten up by a premium on the item itself. This applies everywhere from Amazon to eBay to Zappos.

But it's also true some places have substantially better shipping deals than others, all costs considered. Some may spur you to buy over a certain amount, e.g., "All orders over $99 get free ground shipping". This is tied to the economy of scale, since it takes about the same time to process most orders, but if you have a more expensive order, you (or at least your money) are viewed as more valuable to the company's bottom line.

In those cases, if your order is close to the minimum for free shipping, it may make sense to buy a small, sub-$10 item (also known as a "filler") to push you over the limit. But don't force yourself to buy more than you actually need, 'cuz then you won't be saving at all.

I previously wrote, "Is it worth paying more for faster shipping?". Check it out if you'd like related info.

5. Tax

Death and taxes may be certain, but at least you have a say in controlling the eventuality of the latter — like not paying sales tax if you order from out-of-state. After writing about the Mac mini for Wise Bread, I found out PowerMax, located one state to the south in Oregon, wouldn't ding me for $75 sales tax unlike Apple's own store. Sales tax becomes even more prohibitive on expensive orders: with high-end electronics, it easily runs into the hundreds of dollars.

The point here isn't to deprive the government, but make the smartest decision based on what's legal and available. Be resourceful like MacGyver.

The most important lesson I've learned about modifiers...

is don't get excited until you see the final price. So often, I've thought "That sounds like a bargain!" but by the time I get to the register, all these additional hits, surcharges, and in the case of airlines, hidden costs have added up and stabbed me in the side.

Online, don't be afraid to do a simulation by adding items to your cart and rushing to the checkout to see what it really costs. Some stores add additional friction (whether by dumb design or accident) and require you to signup for account — in which case, if you're understandably concerned about your privacy and getting spammed, have an alternate email address on hand to test the waters.

If you're new to this, the first few times of keeping the above 5 modifiers and other elements straight can be confusing. But persist, know what you want, and get it at a better price than you originally thought possible.

What are your fave modifiers? Have a modifier that I missed? Share your knowledge with us!