Classifieds on Bp.tf at time of writing:

Unpainted:

1 x 2 keys

2 x 3 keys

1 (Spectral Spectrum) x 4 keys

Pink: One for 3 keys and one (Taunt and Fires) for 3.5 keys.

White: One (Kills) for 3.5 keys.

Summary of all the Strange Laws listed for sale on Outpost (http://www.tf2outpost.com/) - excluding posts asking for offers - at time of writing:

Unpainted - 3 keys http://www.tf2outpost.com/trade/25549314

Unpainted - 4 keys http://www.tf2outpost.com/trade/25119787

Unpainted (Level 42, Spectral Spectrum and Horseshoes spells) - 6 keys http://www.tf2outpost.com/trade/25544572

Unpainted (Purple Footprints) - 5 keys http://www.tf2outpost.com/trade/25544952

Purple (Purple Footprints and Voices From Below spells) - 5 keys http://www.tf2outpost.com/trade/25544916

Pink - 3 keys http://www.tf2outpost.com/trade/25571896

Pink (Named, Signed by ArraySeven, Chromatic Corruption, Team Spirit Footprints and custom desc) - Bidding with buyout 8 keys http://www.tf2outpost.com/trade/25588923

Pink (Named, Signed by ArraySeven, Chromatic Corruption, Team Spirit Footprints and custom desc) - 9 to 12 keys http://www.tf2outpost.com/trade/25583133

Lime (Freezecam Taunt Appearances) - 3 keys http://www.tf2outpost.com/trade/25536369

Lime (Fires Survived, Kills, Freezcam Taunts) - 3 keys (and possibly 1 MvM ticket) http://www.tf2outpost.com/trade/25587581

Team Spirit (Kills and Fires Survived) - 2.25 keys http://www.tf2outpost.com/trade/25629947

Team Spirit (Kills and Fires Survived) - 3 keys http://www.tf2outpost.com/trade/25630159

Team Spirit (Named, Kills, Fires Survived Sinister Staining and Gangereen Footprints) - 6 keys http://www.tf2outpost.com/trade/25616662

White (Kills) - 3.5 keys http://www.tf2outpost.com/trade/25612303

Slate (Horseshoes and Spectral Spectrum) - 13 keys http://www.tf2outpost.com/trade/25414415

Other:

(Opinion) As Bill's Hats seem to be decreasing in popularity, I've been seeing more and more Laws on servers I've been playing on, but that may be only a trend on South African servers.

I bought my Team Spirit Strange Law (without the parts at the time) for 3 keys.

(Opinion) I though there are occasionally Laws listed at the BP.tf price, they are usually quickly snatched up - I suspect by people anticipating the price to be going up, or by people dying to get one and snapping one up as soon as they find one at the current "normal price".

The last 5 price votees have all been to increase the price of the Strange Law.

Yes, I know you are not supposed to use SCM due to the fee, but: On Steam Community Market, the cheapest currently selling is $7.15 with Team Spirit paint and Fires Survived. The cheapest pure one is $7.16. Take off the 15% Steam fees and you are still left with $6.09. BP says a key is $2, so that means it is 3 keys 1 ref at Backpack.tf key price. If you take a key at $2.5, then the seller still gets 2.43 keys from SCM.