Used tires are old and usually fly apart faster so definitly you want to look for atleast 1\4in tread left before you consider those tires for an event.
I had a set of 225 45 17 pirelli (spelling) tires with 3\32 left, I lit third gear up pretty good around the oval once then i heard them start to leak air 10 seconds later.
rwdrift likes falken zeix. 400 treadwear, rather inexpensive. I think he said they lasted him some time, in a 205 size.
If you do not burn the tires unnessacarly, like keeping on the throttle after you have spun out, a new set of tires will last a low power car ( na ka ) an event or close to it if tire wear is even.
beware though, you will have alot more grip with new tires compared to ones that are older or used. So if you are getting the hang of drifting on a 205 used or older tire. Dont think you are going to go out and slide the same on a brand new 205. Sometimes its good to have less traction for larger track areas, it allows you to keep in your rpm range easier and allows for more correction with the throttle for steering inaccuracies.
note: a wider tires lasts longer then narrow.