sorry man but that's how it goes in used car goodies, especially wheels and tires.
Lets do a comparison:
guys post below:
Asking $250+ shipping for (So right around 300 shipped):
factory 17" wheels and Michelin tires with ~15,000 miles on them.
OE tires 215/50R17 (Michelin Pilot HX MXM4)
$175 each
Now lets look at your situation:
Asking price TBD
17's with Toyo Proxes 4 with ~7,000 miles
I'm guessin your running this size or close
215/40R17
$120 each
IN SUMMARY:
So you've got half the miles than he does on his tires +1
Chances are your rims are 2 times as old as his (based on mileage) -1
Toyo Proxes are a better tire than OE and are cheaper +2
So I guess you are right you would be the better purchase in this instance so I could see offering an additional $100 based on tire alone.
So I could see offering up to $400 shipped based on condition of the rims. ($400 being no damage to rims, obviously damaged rims bring cost down dramatically no matter what tires)
Let me know if this is more reasonable.