It depends what you want. You can live in SF and enjoy the nightlife, restaurants, shopping, etc. or you can live just outside of town, much of which is suburbia. You'll usually find cheaper rents in the suburbs than in SF.
If you want to live in SF, check out South Beach / Mission Bay
just south of the downtown area. This area is about 10 - 15 minutes from downtown via light rail streetcar. $2500 should cover a 1 bedroom apt.