Proof:

Classifieds:

http://backpack.tf/classifieds/search/id/521e2807ba2536b7728b456b (1 for 1.5 keys, 2 for 1.7, 1 for 1.75, 1 for 1.83 and lots for 2 keys)

Outpost:

Selling:

5.33 ref

http://www.tf2outpost.com/trade/14112518

1.3 keys:

http://www.tf2outpost.com/trade/14218337 (2 days)

1.4 keys:

http://www.tf2outpost.com/trade/14277387 (3 hours)

1.5 keys:

http://www.tf2outpost.com/trade/14246174 (1 day)

http://www.tf2outpost.com/trade/14249054 (1 day)

http://www.tf2outpost.com/trade/14261043 (13 hours)

http://www.tf2outpost.com/trade/14151945 (5 days)

http://www.tf2outpost.com/trade/14197194 (3 days)

1,7 keys:

http://www.tf2outpost.com/trade/14266716 (9 hours)

http://www.tf2outpost.com/trade/14074307 (1 week)

1.9 keys:

http://www.tf2outpost.com/trade/14201060 (2 days)

http://www.tf2outpost.com/trade/14210332 (2 days)

Not trying to remove 2 keys from the range so I'm not providing proof for it. As you can see, lots of 1.5 key sellers so I'm adding it to the range.

Thanks for voting : )