I was in a situation similar to this recently. I was on the recieving end, not the shipper. The shipper also underestimated his shipping costs, but obviously that was his fault. You should have verified the shipping costs before posting, and I can not see your side about losing the 75$. I think his request for the insurance claim is reasonable, even if he got a good deal on the system... (Very nice BTW) The monitors are clearly listed in the original advertisement.
Does the claim with UPS actually cost anything? If so then you could deduct that from the final payment.
In my case we were able to negotiate a reasonable settlement and gave each other good feedback.
:-D
