Range of 23 - 27 keys

There are four total items of the "Berliner's Bucket Helm" with the effect of "Molten Mallard" in bp.tf recorded history. The most recent sale was in exchange for a 20 key (at the time) Pyro Unusual of the "Metal Slug" with the effect of "Molten Mallard" + 10 keys in pure, which I offered for the Berliner's and he had no problem accepting. There was no mention of overpay whatsoever, just a 30 key total trade value.

I was the one who approached him with the idea to trade. There is currently one other user on Outpost in possession of a "Berliner's Bucket Helm" with the effect of "Molten Mallard", and I have provided their Outpost trade in the area below.

The "High Value" is supposed to be the highest past sale, which would be the 30 key total value of my previously owned "Metal Slug" + 10 keys, making for a total trade offer of 30 keys worth with no mention of overpay, but due to my mistakes in calculation of value on the Slug, total for the Berliner's should be 27. The Metal Slug was purchased off of the Steam Community Market for the price of $50 on October 30th, 2015.

Mini for the Metal Slug: http://backpack.tf/vote/id/566bd0e4dea9e9c80a7f791a 18.5 keys

X = 18.5*0.9 + 10

X = 27

Proof of Outpost trade disccusion: http://www.tf2outpost.com/trade/27460286

Proof of other Outpost User selling similar unusual: http://www.tf2outpost.com/trade/27503005

Imgur Link providing evidence of most recent purchase: http://imgur.com/a/TMVT5

Guide I have mainly been using to understand this: http://forums.backpack.tf/index.php?/topic/7-how-to-create-a-good-unusual-price-suggestion/

Previous suggestion along with all of the help from others, once more, thank you again for all the help: https://backpack.tf/vote/id/566bc9fedea9e9190b7f7898