Hotel prices can change by the day, even by the hour. But you can game the system somewhat by using the right Web sites…

1. Air-hotel package Web sites: “Bundling” airfare and hotel can offer significant savings. That’s because travel sellers can “hide” the hotel price within a package so that it’s not so obvious how deeply the room rate has been slashed. For Europe, try Gate1Travel.comGo-Today.com…and BMIT.com. Within the US, look at SouthwestVacations.com and the big sites such as Expedia, Travelocity and Orbitz. Expedia also is good for tropical destinations such as Hawaii and the Caribbean. Compare its offerings with those from VacMart.comBookIt.com…and PleasantHolidays.com.

2. GetARoom.com: The premise here is that some prices are too good to be shown on the Internet. So this company encourages users to call its 800 number (800-HOTELS-8) to get the most deeply slashed rates. Sometimes it works, sometimes not, but it doesn’t cost anything to try.

3. Tingo.com: If you book a “Money Back” hotel room through Tingo, it promises to keep checking the rate for price changes. If the rate drops, it automatically refunds you the difference. Example: One user was recently refunded $153 on a Paris hotel. It works very well on pricey properties, but on midrange and budget hotels, Tingo often doesn’t have the lowest rates to begin with. You might do better at a more budget-oriented site, such as Hipmunk.com or Booking.com.