Link 1: Offered 25 keys (mixed, pure would turn into ~23) and accepted.

Link 2: I found one of the recent owners, Jesterrr. I couldn't get a screencap of the actual trade, but he managed to check what it sold for in his inventory history. This sold for ~27 keys (mixed), which turns into ~25 pure.

TL; DR: The only recent offers that weren't too recent were around 23 keys to 25 keys.