Okay, here is the scoop on my car which has been driven 75% highway @ 65-80 MPH and 25% street. Both my front and rear PS2's have 7/32" tread remaining with 20,160 miles on the odometer. They have never been rotated and are wearing even with no cupping. I have kept the tire pressure at the factory specs of 32 psi front and 33 psi rear. As mentioned above, the front start life with 10/32" and the rear at 9.5/32". With my current wear rate I expect to get at least 35,000, maybe 40,000 from them. IMO not bad at all for a performance tire.

As for replacement cost using Tire Rack prices:

Goodyear Eagle F-1 GS-D3 = $986.00
Front: $188.00 each
Rear: $305.00 each

Michelin Pilot Sport 2 = $1,026.00
Front: $206.00 each
Rear: $307.00 each