Seller at 28:

http://www.tf2outpost.com/trade/27417102 2 days, free paint

Unsold at 30:

http://www.tf2outpost.com/trade/27389944 1 week, free paint

http://www.tf2outpost.com/trade/27419856 2 days, free paint

http://www.tf2outpost.com/trade/27413736 3 days, free paint

http://www.tf2outpost.com/trade/27397542 6 days

http://www.tf2outpost.com/trade/27399797 6 days

Classifieds support:

http://i.imgur.com/99aeWRL.png

2 at 26

1 at 28 (free paint)

1 at 29 (free paint)

2 at 30 (free paint)

Given that the market isn't that large and all the sellers at 28 have free paint, I think the low end from classifieds is reasonable, with a range to be conservative. Feedback welcome