as far as racing goes, cross is one of the easiest sports to get started in. The only pressure really is the pressure you put on yourself. There are beginning fields, and you can pretty much race it at your own pace. (not like road racing at all) There are some heavy duty people out there, but the majority of people are doing it for fun. Maybe your local LBS can loan you a bike? I had a friend loan me one for the first few races, until I got my own. My first cross bike (all I had was a road bike, no mountain bike) was a used bike for $400. It lasted for two seasons and was great fun.

Steph