If you look here under Sold/Expired it at least gives you the initial asking price, not necessarily what they sold for:
https://www.hifishark.com/search?q=polk+srt
https://www.hifishark.com/search?q=polk+srt
Ballpark price ?- Polk SRT
What would the ballpark price of a set of Polk SRT speakers from the mid 90s go for? Minor cosmetic damage. Includes a left tower, a right tower, a center channel, a hollow cabinet, 3 powered sub towers, subwoofer mixer.