I'm currently shopping for a bike, and have been doing a LOT of research. If you want to buy a full build kit, like each piece independantly, your looking at about $1000 for a remotely decent build, minus the frame. That's if you go pretty inexpensive front fork and your building a hardtail. You'll also end up with a bit more nickle and diming going on in the build for tools and cables and all that.
Decent FS frames seem to be a minimum of $500, unless you get something pretty old. If you absolutely have to have a FS bike, I guess you could look at some of the entry level bikes, and then just upgrade parts as they break or you just get tired of something not really working. The frames I've found that seem to be a good price point (pretty much pure XC frames), are the Specialized FSR XC and the Trek fuel, as a lot of people seem to ditch the frames for something better and the entry models are still halfway decent.
Also, check out this: http://wheelworld.com/itemdetails.cfm?id=2898
Combine that with an OK frame, and your looking at a pretty cool entry level bike, albeit heavy.
Hope some of that helps.