If you have no attachment to either coach, then I'd say $100 is a great offer. 1/1 are rare(obviously). But who collects these guys?
And you're not stooging him. He offered. It's worth that to him. WOuld he pay more? Maybe. But that would be pushing the limits of friendship imo.
If it is your ONLY 1/1 then I'd keep it regardless of WHO it is. But if you have others, then this card is nothing special(to you). Nice design. Nice clean (dual) AU. It's really up to you in the end. Check ebay for other 1/1 of similar profile coaches?