Steve, the amount you can expect to spend will depend on the terrain you likely will ride, and the level of quality & durability you want.
I could write a thesis paper on bike fit and selection, but here are the simple points that I always make.FIT
1. You should be comfortable on the bike. That's primary.
2. You need to know not only that you are comfortable in the static position (seated, not pedaling), but also that the fit and geometry mesh well for your riding style and your body type -- including flexibility.
3. XC racers usually like a position that mimics the road bike -- fairly flat back, more weight on the front wheel. Unless you want to race seriously in XC events, skip the "race" fit.
4. Generally, you want to position your hips relative to the crankset in a way that you're not too far behind the crank (excessive load on the quads) or too far ahead of the crank (excessive load on the hammies/glutes). This is determined by the angle of the seat tube relative to the crank, with measurement referring to deviation from 90deg (which would be a straight-up seat tube).
5. Chainstay length affects handling too. 17" chainstays are more stable and are found on many bikes, especially FS models designed for faster riding on rougher terrain. 16.5 - 16.8" chainstays help you climb faster and make it easier to wheelie, but can cause rear wheel hopping at higher speeds on rough terrain unless you get your weight way back.
6. Top tube length, combined with the length of the stem and the rearward sweep of the handlebar, will control the "cockpit" or "front center" length. You can play with top tube vs stem length combinations. I prefer shortish stems (90mm and shorter) for most situations, because I like responsive steering and a somewhat rear-oriented weight bias. However, when I raced XC I ran 120mm stems and 130mm stems for better climbing and flat section speed. The longer the stem, the more weight on the front wheel, and the more "skittery" it feels when descending steeps. Vice-versa for shorter stems.
7. Hardtail vs Full suspension -- this is a comfort and terrain issue. The younger you are, and the more you wish to develop highly refined technical terrain skills, the more I lean toward HT (hardtail). The less flexible you are, the less fit you are, the more rugged the terrain you'll ride, the more I lean toward FS rigs.BIKE SELECTION
1. Continuing from (7) above... A HT rig will teach you BY NECESSITY to choose smoother lines. Whether you want to suffer by getting beat up and bounced around while you learn line selection is another issue. Think of a very stiff (torsional and longitudinal) ski with lots of metal sandwich, trying to ski it in the bumps when you don't know how to ski bumps well. It tosses you about, shows your every balance and technique error, and even can punish you. But when your technique is good, it races through the bumps. HT rigs are just like that. Compare a mid-line FS bike to a forgiving ski that does a lot of things well, but has a somewhat dampened/deadened feel (i.e. K2 5500).
2. Components -- nobody needs topline components. Truly. They are an ego thing. For VERY frequent riders, one step down from the top is best, perhaps even 2 steps down. In Shimano, that means XT or LX, but not XTR. In SRAM, that means X-9 or X-7, but not XO. Then you have to choose shifter types, which means trigger only from Shimano, or triggger OR twist shifter from SRAM. SRAM's trigger is different from Shimano's in that Shimano uses the thumb for one shift direction and the forefinger for the other direction. SRAM uses just the thumb for both shifts.
3. Suspension -- forks and shocks are getting very sophisticated. Which ones to choose can be confusing and sometimes frustrating. Because it's highly subjective, I'd say that you should just go pick out a few different bikes to ride, ride them for demo, and then post your thoughts here. I can tell you a lot more about actual in-use characteristics once you tell me the particular setup. Too hard to go through all of them up front.
4. Cost -- the big bugaboo. Honestly, I think that if you care at all about your equipment in ANY way, you should plan on spending at least $1000. There are decent bikes below that amount, but most of them are relatively poor quality rigs. What you are paying most for is a good frame, and frankly, I don't think that any bikes that retail regularly below $1k have good frames.
Those are primer thoughts. I'll post more as you do more looking into what's available, and post on your own impressions.
Also, re Rio's and aschir's comments...
As Rio mentioned, steel frames are the BEST choice for HT rigs, bar none. You can't duplicate steel's combination of ride quality, affordability, and repairability.
aschir mentioned some bikes down around the $500-700 mark. they will work, yes. if you get serious about riding, you'll want a nicer bike. I assume you will get more technical and serious given your posts re. skiing in this forum. that's why I said $1000. a bike below that point certainly will work, but if you start to take riding seriously, it's got too many weak points, the main of which are the reduced frame quality (uncomfortable ride) and cheap components (wear out with frequent use). for a person who rides one day/week, they would be fine... maybe. [ February 16, 2004, 01:01 PM: Message edited by: gonzostrike ]