Quick! Downvote! A suggestion that's a bit finicky and complicated!

Alright, not sure how this'll go, but let's do it.

(Also, no other recent sales on the Jingle Belt I can find)

Prelude:

Jack Aubrey, owner of the Jingle Belt set offers the chemistry set (built to 137/200) on this trade http://www.tf2outpost.com/trade/26746071

Opening act:

The trade is done: http://imgur.com/dle7ks3 and http://imgur.com/z4gkV4U

The jingle belt moves from Jack Aubrey to Zombie Jesus: http://backpack.tf/profiles/76561198039731024

The sale is recorded thus as 150 keys for the mostly complete chemistry set.

Second Act/ Complications:

I was thinking of doing this for the chemistry set of the item, however seeing as the set sold at 137/200, it seemed closer to the complete item price.

However, mathematically, let's crunch some numbers. 63 x 1.66 ref = 104 ref (or roughly 6.5 keys). This is what it'd cost for the item to be completed from its current state.

Observance of the item http://backpack.tf/item/2546071722 just prior to the trade http://backpack.tf/profiles/76561198036116161?time=1439190000 supports this.

Third act justification and opening to objections.

So the suggestion is that rather then the 150 key trade for the 137/200 complete chemistry set for the Jingle Belt remaining unpriced, I have added six keys to the value of keys exchanged for the set, to theoretically come to the estimated value of the completed item (being 156 keys).

Postscript: Previous sales on partially/mostly completed chem sets have passed also: http://backpack.tf/vote/id/55b80f81ba8d887d228b45a9

If this suggestion is better suited for the chemistry set itself, rather then the completed item, let me know in the comments below.