IMO car hire is best done this end, before you go. Never tried it on arrival though. There are some very good deals, when your plans are more advanced (and I can think straight!) I will let you know where to rent (the cars have always been Dollar but different agencies give different prices).
www.airline-networks.co.uk springs to mind.
£303 is a Good Price. I think the std rate is about £370, but £330 has been available for a while, and BA currently have a January Sale which takes £20 off. The taxes have gone up a lot in three years (now about £120 with BA). You might find that booking a "through" ticket from Guernsey (or was it Jersey?) is cheaper - gab got his end to end flight Munich - Heathrow - Miami (much) cheaper than I paid just for the Heathrow - Miami leg last year, same carrier and flight as me to Florida.
On another note, I was showing Mrs S the race dates for 2006 over Xmas and she said why don't we book a holiday in Turkey to coincide with the 1000km (date to be announced...). Has anyone done Turkey, could it be combined easily with a beach holiday (new thread maybe?)