I hate to be making this suggestion :(. It just seems that vintage hats are getting harder and harder to sell lately, that blue text just doesn't mean as much to people anymore. I was going to suggest 2 flat, but when looking through evidence 2.25 did seem like it could be possible. Let's take a look!

Unsold in Current Range:

http://www.tf2outpost.com/trade/10251165 - Unsold, 1 hour old, buyout of 2 keys + 2 ref

http://www.tf2outpost.com/trade/8960295 - Unsold, 1 month old, many offers of 2 keys

http://www.tf2outpost.com/trade/9993690 - Unsold, 1 week old, offered 2 keys + craft hat

http://www.tf2outpost.com/trade/9499581 - Unsold, 4 weeks old, max offer of 10 ref

http://www.tf2outpost.com/trade/8800137 - Unsold, 1 month old, offered 2 keys

http://www.tf2outpost.com/trade/10099889 - Unsold, 6 days old, offered 10 ref again and Genuine Point and Shoot (1.5 keys)

http://www.tf2outpost.com/trade/6447482 - Unsold, 5 months old, recently offered Vintage Soldier stash (2.5-3 keys) for Tyrant's + 1 key

Sold/Selling at Suggested Price:

http://www.tf2outpost.com/trade/10174645 - 2 keys, received adds.

http://www.reddit.com/r/tf2trade/comments/1chx9g/h_vintage_hats_w_keys_games/ - 2 keys, 4 days old

http://www.tf2outpost.com/trade/10189279 - Paying 1.75, has one in bp so could have been successful.

Many others are just quickbuyers so it's a bit hard to find some real evidence.

Looking to add a bit more evidence, still a bit of a work in progress.