When I got back into riding 6 years ago I hopped on a mid-90's mountain bike, we had old Trek & Specialized MTBs. I rode the heck out of that Trek the first year, it was probably worth all of $350, less now. Now I have 8 bikes in the garage now, a couple in storage, from C&V to carbon fiber. I think starting with a bang for the buck old MTB you find on CL or eBay is a great way to get restarted, don't go spending money on something that will lose half it's value as soon as you roll out of the LBS, and your prefeences are going to change in six months anyway. You can have alot of fun on an old bike, and ticker to your hearts content. No big loss if your "hopefully" doesn't stick.