First of all, what do you plan on doing?
If you plan on riding(which I assume you do) then how much experience have you had? I would ask the owner to ride the horse and see how well that goes. If this horse hasn't been ridden in a few years, he may need to go through a little training. Also, what do you already know about the horse?
Another thing: do you have the extra time/money to care for a horse? Moneywise, the initial price is not what matters the most. There will be feeding, tack, vet, farrier, training, supplies, upkeep, etc. bills.
If this is all fine and dandy by you, then this first horse could be an incredible experience!