[Don Piano]

$100 is the norm for a good regulator.
Tanks which are aluminum will usually be exchanged for steel when you go for more co2 so it is a waste of money most of the time anyway. Steel the shipping sucks. Only thing I can say is that I guess it pays for itself and is best to go get a tank from the local hydro and exchange it for 20-30bones each time, and you never have to worry about the certification (i think 4years is the max) because you get well certified tank everytime. When you are done with it ( if you ever are) you can get your $100 deposit back on the tank.
Cheapest regulator with reasonable shipping I can find is at plantlightinghydroponics.com