It depends on your trails and what you think you want to do... if your experience is limited to something like gravel rails-to-trails roads then stay with your current bike and just maintain it properly. If you think you want to do real trails with steep descents, climbs, hazards etc then I would strongly encourage you to look at a "real" MTB bike. I always tell beginners find the best hardtail in your price range. I recently sold an old Spec. Stumpjumper hardtail for $600. It was in mint condition and fully upgraded to XTR; Fox fork services by Push Industries. The rider will get years of use out of it and using a hardtail to start out will teach you valuable skills that you tend not to develope if starting out on a full suspension bike.

There is nothing worse then cheap full suspension. It can, in fact, be dangerous to ride. A good friend was using his WallyWorld bike on tough trails; the fork pistons (I think he had barely 1 1/2 " of travel which honestly is not really suspension at all) separated from the bike as he was descending and he sutained a serious injury. OK to ride inexpensive bikes, but just know they aren't meant for tough trails.

In the meantime, just start researching what is a good bike fit for you and your riding and then be patience checking CL or eBay or other sources to purchase (like a local MTB CLub website) a used bike. By that time, you will know if you want to commit to the sport and make the investment. Like Clem said, lots of folks have bikes sitting around that need ot be sold. Just know what is a good price and understand components, fit etc. All that is very important.