Gentlemen,
I don't know if you participate in a cylinder exchange program or not, but I just recently had my tanks filled in Edina by J.N. Johnson Sales and Service (Fire Extinguisher service company)and basically, if the tanks are good (stamped within the last 5 years), a 5lb refill was $10 and my 10lb refill as $15.  Much less expensive than exchanging through Midwest or Northern.
 
Contact information for them
4200 West 76th St.
Minneapolis, MN 55345
952.835.4700
 
Just thought I would share...
-Mike


Mike Lebben mike_lebben@hotmail.com