Just as an FYI, I get my c02 bottles refilled at a shop that services fire extinguishers, welding supplies, kegerators, and the like. A google search or yellow pages search for your area should turn something up.
Cost is $7 for a 5 lb refill and $13 for a 10 lb.
Also, the shop I found sells USED 5 and 10 lb bottles. I was able to purchase a FULL 10 lb bottle for about $60 (based on size). While it wasn't as pretty as the brand new shiny 5 lb I bought years ago on the Internet (for twice the money and it was empty of course), it works just as well and lasts a long time.
I realize this is expensive, but is less than buying new, and I wanted to give some sort of benchmark if you are considering a pressurized system.
One other note, the shop had to certify my 10 lb recently as they say it must be done every 5 years. Cost was about $30. Not sure if it is a scam or not, but I have no reason to mistrust the business.
Best of luck to all.