They're using what they know about you
Before you try anything else, try this: Check the price in a different browser. It's not a reliable way to find a lower price, but you might be pleasantly surprised.

Michelle Madhok, founder of shefinds.com, has a simple explanation: Some sites will serve up different prices based on the shopper's location.

"Sometimes it helps to not log in first and see what the price is," she says. But if you log on and find the price to be different, don't rush out the door and try from your folks' place in Evergreen unless you're making a lot of affected purchases. "To be honest, it's usually only a couple of dollars so you'd probably spend more on gas."

You should use what you know, too
"I like to buy online gift cards that are discounted," Madhok says. She uses sites likegiftcardgranny.comandplasticjungle.com.

If you use an HSA for your medical spending, this should sound familiar: You know at least some of the things you're going to spend money on soon, so you can stretch your money by putting it on a card. In this case, we're talking about gift cards to retailers.

For example, if you've got a renovation coming up, you could shop around for discounted gift cards to some of the big hardware and DIY stores. At the time of this writing, plasticjungle.com featured both Home Depot and Lowe's gift cards for around 7 percent off of their actual value.

By the same token, if you know you have a big project or other need coming up, sign up for e-mail alerts from retailers you're likely to turn to. You might receive promotional codes for free shipping or other discounts. Madhok also recommends following the same retailers on Facebook and Twitter for this reason - and trying out the browser plug-in fromdropdowndeals.com. It alerts you to promo codes and coupons available for sites you're browsing.

Online may be easier, but it's not always better
Run or call down to the local brick-and-mortar stores you shop with online to check prices there before buying online. "A lot of times, like at Gap, the stuff in the store is cheaper," Madhok says.

Madhok and colleagues at shefinds.com found one item advertised at a discount through flash-sale website Gilt Groupe -- but found its price was even lower at a brick-and-mortar Saks location.

The best thing you can buy might be time
"I always believe, unless it's something you're desperate for, don't buy for as long as you can," Madhok says. She says that as seasons progress, prices on clothes often drop. The same goes for a lot of products - and best of all, if you wait a little while, you may realize you didn't need that thing at all.

This policy, combined a few price-alert sites and plug-ins, could save you an awful lot of money.