Can you post a bike without a box?

Not really sure, I am hoping that I won't get a ban if i recompense the seller for their ebay fees. But otherwise yes the ban would be for non-payment.

Why don't you start by paying the seller?

If they don't want PayPal do a bank transfer or cheque so that part of the transacton is satisfied.

Then just hop on a train.

Hopefully the seller will meet you at the nearest station which shortens your total journey.