I've heard of people buying used qualifying tires (A6s) from club racing teams very cheaply to use for autocross. Anybody have any experience with this? How many runs could I expect from a set of old tires?

I bought three sets of 245/35/18 V710's from club member Asher. Two sets were 80 or so runs old and one set was 28 runs old. I think I paid $900 shipped for all three. I'm not a national or even regional competitor so tired, old-ass tires don't bother me.

I just finished off the first of the 80+ sets after another 30 or so runs on concrete. I would have gotten more runs had I gotten them mounted inside out. I'll be getting the next old-ass set mounted this week (I hope).

I've heard of people buying used qualifying tires (A6s) from club racing teams very cheaply to use for autocross. Anybody have any experience with this? How many runs could I expect from a set of old tires?

That's a tough question to answer, without knowing how many laps, what kind of car/class (suspension design and weight can really skew wear), and other details...but, if the tires only have two or three heat cycles in them and you can still see the wear bars, you'd probably get enough runs to make it worth buying for $300 to $400/set...I'd imagine.