Well here is my suggestion. USPS I've heard isn't the best on Claims, but I've heard the same thing about UPS. I ship all of my guitars via USPS and they are MUCH cheaper than UPS. I shipped my PRS to Idaho from Florida last week and it cost me around $40 I believe. When you ship a guitar you DEFINITELY want to insure it. In my case I insured it for $1500 I believe.
UPS seems to cost around $70 on average for guitars in cases.
Also, you'll save A LOT of money if you use your own box and package it yourself. They will run you over $100 if you get them to package it.
What dcord said is correct. If you don't have a case, Wrap the guitar in plastic or something(even serran wrap), then make sure the guitar doesnt move around the box at ALL. That means surround the guitar heavily in packaging material(bubble wrap, peanuts, newspaper, etc.
If you have more questions feel free to email me at
evantaucher@gmail.com and I'll get right back to you

Evan