Hollands on Coronado is a good suggestion. You could even walk from the airport terminal to where the ferry to Coronado docks and walk to Hollands. Goggle it. Its not far. Far cheaper than a cab.

Hollands is a privately owned shop that will provide good service. There are other bike shops, but you might get lost in the shuffle. After you pick up your built bike you can camp on the strand and take the ferry back to downtown (15 minutes and $3). Or ride around San Diego bay.