I would go along with the advice given so far. If you buy new, keep the Avons and change to Blockleys after a couple of seasons. The inner tubes will be Blockley tubes anyway which I didn't realise. So that saves you £500 straight off the bat.
Good advice. Use the Avons up and treat them like training wheels. When they're done go to Blockleys or the Coker Excelsior tires.