It's not quite easy to find one for less than 4.33-4.66 without it being snatched up quickly, although there doesn't seem to be much success on that range. There's not that many for sale either - barely a page on outpost.

Instasold for 3.33:

http://www.tf2outpost.com/trade/17634537

http://www.tf2outpost.com/trade/17632672

http://www.tf2outpost.com/trade/17631327

http://www.tf2outpost.com/trade/17626402

http://www.tf2outpost.com/trade/17624337

http://www.tf2outpost.com/trade/17618532

http://www.tf2outpost.com/trade/17615449

http://www.tf2outpost.com/trade/17614971

Sold for 3.66 (or above if stated otherwise)

http://www.tf2outpost.com/trade/17545454

http://www.tf2outpost.com/trade/17617694

http://www.tf2outpost.com/trade/17619086

http://www.tf2outpost.com/trade/17626398

http://www.tf2outpost.com/trade/17625628

http://www.tf2outpost.com/trade/17629091

http://www.tf2outpost.com/trade/17627962

http://www.tf2outpost.com/trade/17632813

http://www.tf2outpost.com/trade/17629679

http://www.tf2outpost.com/trade/17636665

http://www.tf2outpost.com/trade/17640530

http://www.tf2outpost.com/trade/17633305

http://www.tf2outpost.com/trade/17611869

http://www.tf2outpost.com/trade/17612804 - 4 ref

http://tf2tp.com/trade.php?trade=10009427 - 4 ref

http://www.tf2outpost.com/trade/17604599 - 4 ref

http://www.tf2outpost.com/trade/17611141 - 4.33

http://www.tf2outpost.com/trade/17528477 - 5 ref (sold 1/2)

Also:

http://www.tf2outpost.com/trade/17603708 - 6 ref (not in backpack - sold? has a 4 ref offer nonetheless)

http://www.tf2outpost.com/trade/17462833 - 5 ref (willing buyer for 4 ref)

http://www.tf2outpost.com/trade/17620540 - willing to pay 4.33?

http://www.tf2outpost.com/trade/17640805 - buying for 4 ref

I bought mine for 3 ref, 15 seconds after it was posted ( ͡° ͜ʖ ͡°)