I recently bought a small frame road bike for it's components, to use on a larger framed model I already owned.
I have a buyer for the frame on the opposite coast.
I went to a bike shop here and got hold of an bike box which apparently was from a new mountain bike. I had measured the frame's length and height stripped, with the forks removed, and found it needs no less than a 41"x24"x7" box. The one I found, which was the biggest they had on hand measures 47x21x8". I can cut the box down length wise to save on size and weight. I took two boxes so I could combine them for the added height.
My surprise came when I went to figure shipping. The finished packed up bike frame and fork which is now packed in a box measuring 42x25x8", well padded with the dropouts reinforced with wood blocks, and all tubes wrapped in cardboard with several heavy cardboard tubes hot glued in place to prevent crush damage, and the bike frame padded and secured so that it can't move and poke out of the box. The total weight is 14lb 8oz. I tried Fed Ex and UPS, both want over $60, and the PO wants more $107.
I had planned to ship via Parcel Post, since going by their calculator online gives me under $26. When I went to the PO, they measured it by wrapping a tape around the box and weighing it and told me $107, the lady told me that it would have to be half it's size to go at the $26 rate.

Now, this is a small road bike frame, a 21" bike frame, what on earth do people do to ship a large frame or even a whole bike? For one I doubt you could find a box large enough, and second you would need four boxes to make a single box large enough these days. I have a bike frame that I was thinking about selling but the cost of shipping would far exceed the value. It's a 64cm road frame that on a good day would only bring $90 on eBay, the amount of work involved in packing it and the cost of shipping just isn't worth it from what I see.

Does anyone have any better shipping solutions for bikes or bike frames?

I know there has to be some better way because I've won large frames on eBay and had them shipped here with only $18 or $20 postage on them. Are some Post Offices just looking the other way or is there some trick to get those rates?

I just won and received a 63cm frame and fork, it was shipped from Seattle to NJ for $25.67 postage. The guy took it to the PO and shipped it last Monday, it arrived here yesterday. His box was done almost the same as what I've done with the bike I have to ship, only much larger. How do others get these cheaper rates?
Someone told me that I could get cheaper shipping if I used one of the various shipping stores but those that I called were all more than double the prices I got shipping it myself. They may get a cheaper rate but they don't pass it on to the customer from what I see. I even went to a local bike shop who I deal with all the time, he offered to ship it for me under his UPS account but the cost was only a few dollars less, and to be honest, I'd rather not use UPS due to past damage issues.