Previous suggestion got through based on a QS. 3.5 is too low, I know from experience on this hat. See the notes for proof. This range is much more reasonable.

The last suggestion was based on this QS:

http://www.tf2outpost.com/trade/8154525 he was only asking 3.66. I almost bought this b/c I know it was a good deal.

Here's the proof:

My trade:

http://www.tf2outpost.com/trade/7741562 (3 weeks ago)

-SOLD for: 3 buds, 100 ref and 3 keys (~4.25 at that time b/c keys were like 3.33)

-Was offered about 4.6 pure originally, but he found another seller that was only asking for 4 buds. All other b/os were 4.5ish at that time.

I was also offered:

-Self made key for the SNS and the brainiac. Sold the SNS for 2.9 pure so that offer was about 7 buds imo, making the Brain 4 buds

-buds, 23 keys, black bills, ts bills, SF huntsman for brainiac

(He added to this offer in chat, it was something like bud + 36 keys + w/b/TS bills + SF huntsman = ~3.9ish)

I bought mine for Ghost crown + bubbles samur-eye (3.2 + 1.3 = ~4.5)

http://www.tf2outpost.com/trade/7376790

Cainisable sold his for a GE snaggle + a bud (~4.3) to Snazzy

(i know this b/c he's on my friend list and we both owned a brainiac at the same time)

-before trade: http://backpack.tf/id/76561197996098187?time=1356768000

-after trade: http://backpack.tf/id/76561197996098187?time=1356854400

Snaggle & bud history:

http://backpack.tf/item/408669489 Snazzy to Cainisable

http://backpack.tf/item/92256492

Brain history:

http://backpack.tf/item/1276644360 Cainisable to snazzy

MANY collectors go for these to combo with beams, Moon hats, o fire, energy etc. to do the galaxy thing. Especially b/c of the whole Einstein connection.

So this is 3 documented trades of 4+ for this misc vs. 1 QS @ 3.66.

I know there aren't many good offers on the current trades, but they are also fresh and this IS an engie unusual afterall. From my experience with engie hats, they tend to sit around with no offers and then "boom" you get your b/o.