Thanks again for the input, it's really helping a lot.
Apparently he did use to be racehorse, to what extent I am not really sure and need to speak with my trainer more about it.
After researching horses for sale in Texas (I'm in Austin) here's just three that I found comparable. The only exception being that you don't quite know their temperament until you ride them.
Gentle 16.2 TB Gelding Hunter/Jumper. - PeterPan
Refined Beautiful Jumper Currently showing 2'6" - Lil Miss Chris
Great personality, talented jumper, will take anyone around! - Monkey
Granted, some of these are a bit older then my potential horse.
So I guess my next move would be to offer something around $5000-$6500. I just feel bad offering less then half of what he's offered at and explaining that I think they way overpriced him. The seller is also my trainer.