This site is good for shopping for a car by insurance group:

http://www.abi.org.uk/carinsurance/default.asp

You have probably already shopped around for insurance but I would definately recommend not stopping until you have had a dozen quotes - usually the cheapest you find will be the cheapest by a long way. Current cheap places I have heard about are elephant.co.uk and Tesco.

BTW, engine size doesn't make a lot of difference in some cases - I have a 5.0 and a 5.7 V8 insured for under a grand total with 1 yrs NCD on one and 2 yrs on the other, and have been driving for 3.5yrs (and am 24). The fuel costs outweigh it of course, although I did get 22mpg out of the Camaro when buzzing down to Dorchester and back yesterday.

Gareth