Alright, let's give this a shot.

Just bought two of these cute little guys for 5 ref each within the last few hours:

http://www.tf2outpost.com/trade/23440991#latest

The state of classifieds seems to back up my price, however minutely.

Classifieds at time of suggestion:

1 at 5 ref, 2 hours

1 at 6 ref, 21 hours

1 at 12 ref (1.2 keys), 44 minutes

Outpost at time of suggestion:

Buying:

4 ref: http://www.tf2outpost.com/trade/23441283

4 ref: http://www.tf2outpost.com/trade/23475164

Selling:

Offers (denied 1.66 [ref?] offer): http://www.tf2outpost.com/trade/23439408

8.55 ref, 1 day: http://www.tf2outpost.com/trade/23459726

10 ref (1 key), 13 hours: http://www.tf2outpost.com/trade/23493123

10 ref (1 key), 2 days: http://www.tf2outpost.com/trade/23453518 (same person as 5 ref classified)

10 ref (1 key), 3 days, unbumped 18 hours: http://www.tf2outpost.com/trade/23422536

20 ref (2 keys), 4 hours: http://www.tf2outpost.com/trade/23501411

20 ref (2 keys), 3 days: http://www.tf2outpost.com/trade/23433371

30 ref (3 keys), 3 days: http://www.tf2outpost.com/trade/23424016

40 ref (4 keys), 3 days, unbumped 3 days: http://www.tf2outpost.com/trade/23422727

All in all, a lot of variation because of new Halloween item hype and general lack of price but some clear patterns forming around 5 ref.