USPS (not UPS) Global Priority is the way to go. I’ve had a few large frames sent over and even a whole bike split into two boxes. A frame should cost about $50-60, and the bike was $130 inc insurance. It is vital , though, that the frame is packed as small as possible. an inch too big and the price can double!
Check the USPS site for size limits.
It is possible to insure the frame using this service but it is not tracked – something the sender might baulk at. Some are game, some aren’t.
Allow another 20% for customs duty this end. It might slip through, but probably won’t.
It may take 2 or 3 weeks to get here, but I know of one instance where a frame arrived the next day!