Don't feel bad. He is a grown man making his own decisions. He knew he was selling it cheap and knew that he would sell it cheap to anyone with the cash. For all you know, he might have tried to sell it already for more and couldn't. Maybe he needs the cash now and can't wait for a better deal. Regardless the reason, the man named his price and you paid it.
If he ever needs a favor that you can do, remember this deal and help him out. It'll make you feel better knowing that you will help when he needs it, and he will be ok knowing you are a good friend and not just someone taking advantage.
If he ever needs a favor that you can do, remember this deal and help him out. It'll make you feel better knowing that you will help when he needs it, and he will be ok knowing you are a good friend and not just someone taking advantage.