Matt Gross of the NYTimes has a regular column called The Frugal Traveler. His column in today's (March 15th) issue is titled Frugal San Francisco where he used AirB&B.com, just about the cheapest way to stay almost anywhere, even in expensive SF.

The most expensive thing about traveling is meals. Use Yelp for recommended inexpensive dining options, they've got the most extensive database on smaller restaurants that no one else really covers. Some recommend Chowhound but I've never found it terribly useful. Yelp is easier to search and use. We found some great places in the little-known Columbia City neighborhood of Seattle through Yelp. For that high-end splurge I use OpenTable, where making a reservation is quick and easy once you register, and the feedback is extensive from fellow foodies.

The Internet makes doing research easier but it still is time-consuming. But spending the time on sites like TripAdvisor and Kayak can really pay off once you're there. Good hunting!