Hi Steve,
For your first season (or at leas the first few races) you could get away with using someone elses Scrubs unless you're planning to win first time out!
This will save a fortune and if they were good enough for the other persons last lap then they'll be good enough for your first few.
The top of the list seem to be the SC pro (diablo), Racetecs, GP racers or Power Ones. I don't know of anyone racing on Avon Extremes.
A used set of Racetecs will set you back about 40-50 quid. A used set of Power Ones will set you back about 90 quid. So if you are going to buy new tyres you'll get twice as much for your scrubs if you run Power Ones! Worth thinking about!
There's a place on the net selling Pirellis for £199 delivered (can't find the link at the moment) and there are various sellers on ebay selling new fronts at £40 for the GP racer etc.
As to which one you can go faster on, that will be down to your personal feel for each tyre.
For wets, Pirelli/Racetecs are virtually the same tyre and the Dunlops always get very good reviews. I haven't seen a review or heard any comments about the new Michelin wets.
I have a spare wet front (120/70) that you can have for the price of the postage if you like?
C