The cheapest way I have found is to buy from Grafand sons by the case [10 cans ] I got a case when it came out and it cost me 32.80 a can that way that includs hazmat and shipping.
Also of interest is the fact that all my and most other Close breach TC'sshoot the 250 SW and short black Harvestor sabot with a heavy load of BH to less than a minute of angle. If you have an Outdoor Sportsman store close by I hear they are sell BH for 29.88.
http://www.grafs.com/powders/3523
Link to where I get mine. Lee