1. Have you looked at Delta Cargo/Delta Dash? I've used that before with pretty good results, rates look pretty good. Perhaps your father's employee benefits extend to that? Delta Dash is quoting $93 for 51-70 pounds, about $70 for under 50.
2. Otherwise, I'd get a DL Amex, pack it up (retail packaging, if available would seem to be the best option to me), and check it.