Hello, I am very interested into getting into the world of trials (and maybe observed trials competition).  I am now a B Class Motocross racer looking for another motorcycle sport to attempt, and trials has very much intrigued me.  I am looking to buy a motorcyle shortly (because fall seems to be the best time to buy a motorcycle).  I have found several in my area, but are looking for some input. 
What size bike should I be looking for?  I am 6' 1" and weigh 215 lbs without gear (athletic ) 
How much should I look to spend on a decent bike?   
I know what a MX bike would cost, but trials seems to be their own market by far.  I am looking at a couple bikes here locally and they seemed to be priced more than KBB and way more than NADA.  What would most people value a 2000 Gas Gas TXT 321?...KBB says $1900, NADA is $1000...I have no point to understand if I will be overpaying...any suggestions? 
Thanks!!!!  I look forward to riding trials.