First let's start by noting there are only 22 of these according to #1. Currently there are three sellers on tf2op trying to move these.

#2 shows a level 42 selling to someone who is now trying to sell it for even more. From what I could determine, these are the items he traded for: 1 Strange Widowmaker, 1 Genuine Short Circuit, 10 Pencil Pushers, 1 Dr Dapper Topper, 1 Minigame, 1 Sticky Jumper, 1 Halloween Potion, 4 Halloween craftable items, and 24 weapons. All of this comes out to about 43 ref, let's say that's about 15-16 keys. In one of his older trades, he was offered a Fetti Tyrant(1.7-2.2 Buds) but declined. It's hard to say whether or not they were offering on one or both of his dirty Ketche's

Link #3 shows a dirty level 100 Ketche with a current offer of 5 Buds. The owner traded a Stormy Storm Raincatcher (2.1-2.7 Buds) with the belief their friend was going to buy it from them, however that did not happen. Not going to let this one affect the price too much since it's level 100. This site multiplies the price of vintage hats x6 when they are level 100. Unobtainable uncraftable hats that are also level 100 could be valued similarly, but most likely less than x6.

Say that we did take the current price of Buds (25-26 keys) and multiply by 5 for the number of Buds offered (125-130 keys), then divide by 6 to take the value of "Level 100" away, we would have 21-22 keys. Of course if we do this for the Stormy Storm Raincatcher the current seller traded, we'd get about 11 keys.

Ranting aside, there are 3 sellers on tf2op. One bought his for 2.1-2.7 Buds, has an offer of 5 buds, but his is level 100. Another user sold his for items adding up to about 15-16 keys, his also had a special level but I guess it didn't matter. Then you have old offers of 1.7-2.2 Buds for presumably a pair of dirty Ketches. Another Ketche with no offers. Then a new member to the Ketche group trying to move his new Ketche and has yet to attract offers. Instead of putting a giant range on this I'm going with a little bit above what I could confirm the sale went for (could have been something I missed, but nothing big ticket it seems).