Always amused by people who b!tch about the cost of the Avons. Many are the same people who brag about an engine mod they did to take it to "600 HP', "700" etc. but they won't spring for tires to ACTUALLY make the power usable. Heck, 450 HP with BFG TAs is not usable. Everything your Cobra does must be done via four relatively small contact patches of rubber; acceleration, braking, turning, are all dependent on the tire contact patch.
Put the best you can afford on the car and consider it an annual expense, i.e. if the tires are $1000.00 and you change them out at 5 years it was $200.00 per year just like your
oil and filter. More than 5 years on a performance tire is asking for it. The argument "it still has good tread" is facetious, tread depth does not guarantee tread performance as tires outgas and harden over time.