I don't know what those games are going for in your neck of the woods but $2200 seems high for a non-working game that you have an inside track on.
If you can't find local price references on Batman, your customer/seller likely can't either. I wouldn't pay more than $1500 US for a non-working Batman and even that would be a stretch. It's not a great game and those early DEs are not of very high quality build wise.
Sellers are always convinced you are gonna make huge money when you fix it, but it's not that easy. Might be too late at this point but I'd try to get the seller to see it my way or move on. Why bail them out of their headache? They own a broken Batman, not you. They should be happy to get rid of it.