It hardly comes as shocking news that luxury watches tend to be expensive. Panerais, Patek Philippes, and Rolexes retail for thousands, if not tens of thousands, and are built to be passed down from generation to generation – which is wonderful if you're ready to make a significant investment and less-than-wonderful if you're just looking for a timepiece to flash around for a bit. High costs have traditionally led to prolonged windowshopping and capitulation (in the form of a trip to Casio), but new websites are now making the used watch market more transparent and accessible for first-time buyers.

"Before the Internet, people really didn't know what their watch was worth, whether they were buying or selling," says Paul Altieri, whose site, Bob's Watches, lists Rolex timepieces with both buy and sell prices. "Dealers would sell $5,000 watches for $8,000 after buying them for $2,000."

According to Altieri, more Rolexes (and more money) are now changing hands on eBay than in licensed dealerships. But a number of sellers on the site are actually dealers trying to muddy the waters by presenting themselves as collectors. Altieri's elegant solution, extreme transparency – "the difference between the buy and sell number is our profit and some parts" – makes the simple arithmetic that justifies buying a used Rolex much clearer.

The math works like this: A watch that sells for $12,000 costs a dealer $7,000 wholesale new, meaning that if a watch enthusiast purchases a new GMT-Master II and wears it for a week, the timepiece has already lost roughly $5,000 in value (the buyer has parted with the money for sales tax as well). That said, certain vintage models go up in value as they become rarer and rarer. The short game doesn't work and the long game is a gamble. The question is how exactly to make a mid-range investment.

According to Altieri, the answer is to look for specific models that are always in demand. The ultimate example is the Daytona models, which are perpetually in high demand. A used Daytona Cosmograph or Daytona Panda Dial won't lose value quickly, as a new watch would, and the reliable resale market means that buyers can rest assured that they'll be able to unload it without taking a huge hit. Also, with a classic dial design, three subdials, and a graceful arrow for a second hand, it's a great looking watch. The timepiece looks smart itself and marks its wearer as a savvy investor.

"With the Daytona, it just feels like every year there are fewer to go around," says Altieri, who, as a collector, sometimes gets too attached to watches to sell them. "I'm good at buying them and not at all good at selling them. The money is uglier than the watches." [Daytonas from $8,695; bobswatches.com]