Is there a bus you could take?

Sadly Estartit is not famed for it's excellent bus links!

Renting a car for 1 day could turn out expensive.The Costa Brava in my experience is one of the dearest places to hire cars.
The only place I know of is Rent Services on Ave Grecia Estartit.
You will need your passport, drivers licence and credit card.Debit cards are not normally excepted.
Also bear in mind some small businesses rentals.When they say a days rental, its office opening to same day closing,not 9am to 9am the following day.

Probably won't be bothering now to be honest, i've told the wife that if she can get 3 weeks off next year, we're driving there!!!