You can get a 3/4/5/6 year old bike for not much. Mine's an 09 Beta Evo 250 - much better than I am. Avoid 03/04 Gas Gas as apparently their gearboxes self destruct..

How hard can it be? Extremely is the answer. Forget everything you've ever done on a bike and have a go. It's hard - really hard and the whole concept is bizarre, but it's great fun and dirt cheap. Events seem to be everywhere and this Sunday I was 10 mins from home, grounded the car on the way in and got towed off by a quad. Fell off into both mud and water and had a generally great day's riding...and was home by mid afternoon.

Have a go.. You'll not regret it!