As far as I'm aware, once you win an auction, the seller can ship at the listed price, ask you if you're willing to pay more, or cancel the transaction. Best case, you get crazy cheap shipping. Worst case, the transaction gets cancelled and you're not out a dime.

I once bought a 36" x 16" bass drum on eBay, listed with a shipping cost WAY lower than I thought it should be. I had a feeling that was the case, but I bid anyway in case I might get a bargain. The day after the auction closed and the seller got sticker shock from FedEx, UPS, and the USPS, I spoke to the poor girl (and her father). She asked if we could cancel the transaction. I'm not a jerk, so I said yes, and we all moved on. No harm done.

If you want to be proactive, you could use the "ask the seller a question" function on eBay and inquire about shipping. (And packing, so the bike doesn't get damaged in transit!!!) You could even suggest some low cost shippers like bikeflights.com or shipbikes.com .