2 month old price; might as well update it. From looking around Outpost, it seems that 13 is no longer existent with these Coupes.

Classifieds:

http://backpack.tf/classifieds/search/330/5/34 - One seller at 11 and 1 seller at 13. The seller at 13 hasn't bumped in 2 days.

Sellers:

http://www.tf2outpost.com/trade/12658348 - Offered a Bud for the Coupe + any Scout Unusual (Owner claims to have seen Bombing runs go for around ~10 keys, so the Coupe is being priced at 12-13 in this case). Owner seems interested in the offer.

http://www.tf2outpost.com/trade/12928484 - Offered a Black Bill's (around ~8.7 keys) + V. Baseball Bill's (1 key) + Kringle (1.3) (around 11, 10 after overpay), but was rejected.

http://www.tf2outpost.com/trade/13255303 - Same person who's selling for 11 here is selling for 12 on Outpost. Weird...

Sold:

http://www.tf2outpost.com/trade/12609846 - Quicksold for 11 keys.

http://www.tf2outpost.com/trade/13246110 - Owner's backpack is private, but he most likely sold for a Bubbling Ketche since he has a trade looking to swap another Unusual for it. After overpay, the Ketche is 11.7 keys.

Conclusion: A small market these things have, as you can't track history that's not 2-3+ months old that's of any use to you. Feel free to provide counterproof if you find any. Thanks for your time.