Needs a suggestion, thought I'd give it a shot. Had to rely on SCM since I don't have premium, so any additional evidence, either in favor of, or to the contrary, would be greatly appreciated.

If I've done anything wrong with my method, please let me know.

http://steamcommunity.com/market/listings/440/Strange%20Tartan%20Spartan

Sales between February 20th and March 17th were between $5.00 and $5.40. Since then, there were two sales at $3.36 and $3.85.

Treating $2.49 as the price of a key, the low value is about 1.35 keys, and the high value is about 2.16 keys. The mean dollar value about $4.75, and the mean key value is 1.9k.

Recent Sale occurred at $2.73. Considering it an outlier, as it appears that it was someone filling a buy order.