San Francisco is suffering this interesting evolution in food/resturants. The prices are going up, but so are the portions. Some stuff is still "height-of-dot-com" expensive and a lot of stuff is "dot-bomb" collapsing.
If you go to Chinatown (Stockton or Grant Sts in the North Beach area) you can find traditional Chinese food and reasonable prices. Walk up and down the streets and read the menus posted outside the various establishments.
EVERYTHING at Fisherman's Wharf/Pier 39 is over-priced, heavily-tourist-oriented. Walk along the Bay towards Ghiradelli Square and grab something with crab from the little stands outside on the piers. Chances are it's only been out of the water for a few hours.
All around Union Square is a mix of moderate to high price, due to the proximity to the Financial Dist, the shopping center and the large number of tourists.
If you have a specific ethnic food you like, or if you are headed to a certain part of town, I can narrow it down for you a bit more.
- Rae