Please read all before voting. 2 Month Old Price. A pretty rare strange and only one page on the Outpost. Hard to scrap up proof.

On the TF2 Outpost...

http://backpack.tf/classifieds/search/Blood%20Medi - One seller selling for 4 Keys.

http://www.tf2outpost.com/trade/11544771 - Same as above.

http://www.tf2outpost.com/trade/11320195 - Offers of 26.66 Ref (5 Keys), 5 Keys Pure.

http://www.tf2outpost.com/trade/10689615 - Offer of 4 Keys + a craft hat. Declined.

http://www.tf2outpost.com/trade/11392212 - 5 Keys. Unsold for 6 Days.

http://www.tf2outpost.com/trade/11254496 - Offer of 4 Keys. Declined.

Looked at the TF2 Trading Post to see if I could find more proof:

http://tf2tp.com/trade.php?trade=9520963 - 5 Keys or 4 Robo Keys. Unsold for a day.

http://tf2tp.com/trade.php?trade=9513384 - A guy selling for 4 Keys

Some had no offers. Maybe due to lack of interest?

http://www.tf2outpost.com/trade/11518670 - No Offers

http://www.tf2outpost.com/trade/11518014 - No Offers

http://www.tf2outpost.com/trade/11328311 - No Offers

CONCLUSION:

Offers and sales seem to range in between 4-5 Keys. People are willing to drop to 4 Keys to sell this rare strange.