Cycling used to be a big part of my life - I worked in bike shops for quite a few years through high school and college so am a bit biased towards buying from a bike shop vs. department stores. After a long layoff, I've been getting back into it the last couple of years and my wife and I recently bought Trek mountain bikes from a local shop. I personally wouldn't buy a bike without test riding it first (no different than buying a car or truck) but that may rule out the department store / mail order options. If you have access to a decent bike shop, you can test ride a few to get a feel for how a $400 bike rides compared to a $4000 one which may help you determine a price range you're comfortable with. You also may consider renting bikes for a day to get a feel for what it's all about - the shops here will apply the rental fee towards a purchase if you end up going that route.
