I don't know -- obviously you know the guy better than we do, but it almost sounds like he's giving you the part. You keep raising it with him, and he keeps giving you some nonsense excuse about why he can't take your money. If he wanted your money, five seconds on the internet would give him a price. Or he'd just say "look, I probably paid $30 or so -- if $30 is ok with you it's ok with me." Instead he's got to track down some mysterious document buried somewhere in a vast warehouse or his dog ate it or...who knows what. Now, it'd be better if he just came out and said "look, keep it, it's on the house," but he might feel awkward or something.

So I say drop it. If one day he asks about the money, you can say that you'll bring it by -- even if he does get around to quoting a price, it's not like he's going to suddenly demand that you fork it over right there on the spot. But if you feel awkward about it, just ask him -- tell him you don't like feeling like you owe anyone money, and just want to know if he wants you to pay him for it or not.