I have sold several planes on eBay and shipped them successfully. These planes are really easy to pack and ship. First off, UPS and USPS are out as shipping options since the wings will make the package to big for either of them and you should know this now rather than later. But, there is an even better option for you - FedEx Ground service will ship very large boxes and charge only by weight without any extra charge for large boxes. Greyhound will also ship them at a very reasonable rate but you have to take it to the terminal and the customer has to pick it up at the terminal - a consideration.
Now as to packing, you could just take it to a packing service that has FedEx pickup (check FedEx's web site or the Yellow Pages for the one nearest to you) and have them box it and pass the cost on to the buyer. One of the basic de-facto traditions of eBay is that the buyer pays all packing and shipping costs, so you are not out of line asking that and buyer's are expecting to pay a reasonable fees for it.
Or if you want to pack it yourself, you just measure the tail; find a box the tail fits in with a bit of padding and three or four boxes the same size. Two of them become the top and bottom of your box, and the others are opened and telescopes and taped to your top/bottom boxes forming a single tall box! Then some bubble pack or crumpled newspaper or foam to block up the fuselage from the bottom (helps to pull the propeller and you do want to pack it so that the nose is down, not the tail), and slide in the wing (if your wing is a two piece, wrap the two halves with padding into one unit) and slide the wing in - it usually will fit under the landing gear. It's OK for the plane to have the landing gear touching the box walls if there is a little "give" above the plane. After all, they are designed to take a hard landing. And you are there with tons of extra room to put in well wrapped accessories.
Wrap and block the tail surfaces well, this is the most delicate part of the plane and the most likely to get damage if they turn the box upside down. You can help to keep this from happening (the tall box is the first major step) by putting address labels and the such up on the top sides (not on top) - this way, it has to stand on the bottom to be read.
You do want to make sure there is no fuel in the tank, and little thing like any loose items you are including like a starter, or battery are secure enough that they are not going to take of in transit and "carve" a path of destruction through the box, but this is not usually a problem.
Oh, MOST IMPORTANT - make sure you have it insured (you pass the cost on to the buyer as part of the shipping cost - just include it in the cost). In all shipping, it's the shipper that is the insured party, not the buyer, so protect yourself.
Ron Bennett Monmouth, OR