Got 2 225/40/18 tyres which i have just changed. They are the original Sport Contacts which came with the car and have 4mm left.

About 1/4 to 1/3 of what they cost new - provided no uneven wear, sidewall damage or previous repairs.

I'd steer toward the 1/4 as buyers will also be factoring in the fitting when it comes to judging how much of a bargain they are.  2.3mm left of tread VS around 6mm of tread (excluding limit) as new.

Got 2 225/40/18 tyres which i have just changed. They are the original Sport Contacts which came with the car and have 4mm left.

£30 each, £25 a tyre part worns from any local tyre place.

Ended up selling them for £40. Put them up on Gumtree and they werew picked up 50 mins later