My last holiday was here...
http://www.emiliosbar.com/ Fly to Jerez from Stansted (about £12 each) and it's about 20 miles in a hire car (about £100 a week) and the apartments are about 2 miles from Cadiz for going out etc, but they're based in a very secluded and quiet port. The owners Emilio & wife (forget her name) have a little bar there too. We had the cheapest apartment, about £180 I think.
You'll have plenty of spare wonga from you £600.
or....
How about one of Dickieducati's Croatian apartments???