would you not consider getting a classic car and going on classic car insurance? you'd have to ring direct for quotes seeing as you are 18 years old though. mind you, if classic cars do not have enough 'street cred' for you, then this wouldn't be a solution......
if you do not mind having a tracker fitted and driving limits imposed (ie, 11pm-6am is a no-go), then perhaps try co-op young driver insurance. their price is a bit stupid if you just insure yourself, but if you have the maximum 3 named drivers they allow it fall considerably. parents, other family relations - hell, even add your elderly neightbours ;D however for them the car has to be from year 1997 or newer; also if you can't afford a car of more than £2,000, then cars that are in this budget and cheap to insure are skoda fabia, fiat panda and seat arosa. mmmmmmmm.
......apparently if the blackbox reports you to have good driving style, they can refund you up to 11% of the price you paid - however if you drive sh*t, then you have to pay around 15%-20% extra on the original quote, or they cancel it altogether ;D