I find that the online calculators for Fedex and UPS are pretty accurate these days; unlike a few years ago when you'd get a spectacular price with the calculator and find it's triple that when you go to ship.
Weight doesn't seem to change the price much between 30 and 60 lbs, it's mostly box size. It depends on where you're sending it to as well, of course. From Michigan, I can usually send a complete bike from between 35$ across a couple state lines, to 80$ to California. Bare frames are nice because you can use a very flat box and you can ship those quite fairly if you can get a box to hug it tightly: 15-30$. Most whole bike boxes are in the vicinity of 54x9x28" and you can get them free from bike shops.
USPS is actually moving more towards the UPS/Fedex dimensional weight model and they actually gave me the best rate (by far) for the last bare frame I sent. I always check all three with the online calculators and prefer to go Fedex if they're all close.