I have shipped frames as large as 25 inch in a 108 inch box (girth plus length). Check USPS parcel select rates, but it is in the $20 to $25 range. Cross the 108 inch size, and rate goes up a lot (like double to triple).

Bike boxes are a LOT bigger than 108. You have to cut them down in all three directions: height, length and depth. I have a before and after pic of a cut down box on my Facebook bike page.

Note, 90% of what I know about packing a bike came from Miami Jim, the other 10% from Randy Jawa. Do a search for Jim's packing thread, its worth a read!

In the 108 inch and smaller size, I find the post office has the lowest rate. From 108 inch to 132 inch, Fed Ex has the best rate (open a Fed Ex account first, through your ebay account). Over 108? Cost goes way out.

Don't forget to cut the depth of the box! A lot of boxes are 8 inches deep (measured on the outside). The girth measurement doubles the height and depth. Cut the box down to 6 inches. Because of this "Doubling", that saves you four inches against the 108 limit.

My last shipment I cut the box down shoe box style. That means two pieces, a bottom section and a lid. What a PITA. But it allowed me to fit a 25 inch frame set in, no problem. Up until then, the largest frame set I fit in a 108 inch box was a 24 inch.