An alternative for those looking to set up a new (and/or small) pressurized CO2 system is the new regulator from Red Sea. They have a version that uses paintball cylinders.

I didn't want a big cylinder sitting around, plus I didn't want to drive all the way to nearest industrial welding and gas supply shop so I got this one. It came with a needle valve for control and has been working pretty good so far. My cylinders are only about 12" tall and 4-5 inches in diameter so they hide nicely behind the tank out of sight.

Aquarium | CO2 System Components | Co2 Pressure Regulator for Paintball - AO0615 - ThatPetPlace.com

There's plenty of paintball shops around and I can get my 20oz cylinders filled for $2-$3. It lasts between one and two months on my 50 gal tank depending how high I have the flow cranked up.

You can get cheap paintball cylinders on e-bay ($10 or less for 20oz). I've got two so I always have a back-up. That way I can switch them out if I unexpectedly run out of gas and I don't have to rush back to the store for an emergency refill.

Downside is larger systems may burn through 20oz cylinders kind of quickly.