I made a mini on this a while ago, I just have been too lazy to make a suggestion for it until now XD. Over a year outdated. I got 3/4 of the way done and then I refreshed my browser... Re-suggestion at a probably better range.

Recent sales

Sale 1: http://www.tf2outpost.com/trade/22860820 Sold for a Nuts and Bolts Katyusha, which I updated recently at 12 keys. I believe because it was offered, it doesn't need overpay? Correct me if I am wrong.

Final sale: 12 keys

Sale 2: http://www.tf2outpost.com/trade/22970442 Sold for 16 keys pure, thought the user wasn't Outpost banned at the time, I think the sale is still valid.

Final sale: 16 keys

Sale 3: http://www.tf2outpost.com/trade/23761353 A very complicated sale, it sold for 71 ref, which using the converter, is equivalent to 6.52 keys rounded to 7 keys (I wish .5 keys were aloud sometimes), plus the sweets of a Huntsman's Essentials, which is worth 2 ref, a Strange Market Gardener, which the most commonly sold price in that range is 1.66, a Strange Crit-a-Cola, which is equivalent to 0.33 ref, a Genuine Wilson Weave painted purple, which he is the only seller of that I could find, so counting it at 2.66, his price, and a Prof. K.S Diamond Botkiller, which I couldn't find any sales on Outpost for, most commonly has sold for around 11 dollars on SCM, equivalent to 5.05 keys, rounded to 5 keys. (The items are still in the new item section of his backpack, thought note that not all the things in there were from the buyer) 7 keys+(2 ref+1.66 ref+0.33 ref+5 keys)*0.9=12 keys, his B/O, just not all in pure.

Final sale: 12 keys

Sale 4: http://www.tf2outpost.com/trade/22968865 Bought for a Stormy Storm Berliner's Bucket Helm (The item histories: http://www.tf2outpost.com/item/440,3029363018,30049,5 the Toque, http://www.tf2outpost.com/item/440,3029363005,303,5 the Helm) Mini at 15, 15*0.9=13.5 keys

Final sale: 13.5 keys

Mini on the Bucket Helm:

Only recent sale I could find.

http://www.tf2outpost.com/trade/23561012 Sold for a Stormy Storm One-Man Army, and a Strange Quick Fix, thought the Quick is less than a key rounded (Item history: http://www.tf2outpost.com/item/440,3200695165,601,5 ) Valuing it at 1.1 buds, which was 17.25 keys at the time of the sale, rounded to 17 keys 17*0.9=15.3~15

Mini value at 15 keys.

Current sellers:

http://www.tf2outpost.com/trade/22980491 Unsold at B/O 12 keys for 1 month, proving that 12 keys is not an outlier

http://www.tf2outpost.com/trade/23799579 Wants offers, 16 key B/O thought not bumped well.

http://www.tf2outpost.com/trade/23245865 Taking offers

One on the classifieds for 15 keys, the same guy with the 16 key B/O on Outpost.

With sales at 12 keys, 12 keys, a long unsold at 12 keys, a 13.5 key sale, and a 16 key sale, 16 keys seems like a slight outlier, and the seller was Outpost banned too for scamming, 12 to 13.5 keys seems like a good range.