Dont be sorry about the Grainger deal. I was out nothing but the time to order. As my brother would say " The Juice was worth the Squeeze" I'll call the place you recommended tomorrow. I'm thinking I want a 150CF bottle. Victor was $250 and Wilbanks was $227 ( though the company I work for has an account there so I might be able to get it a little cheaper). Both places said that they were in the 25 dollar range to fill (swap) the tank.
It is my understanding...
Flux wire welding is not nearly as good looking or controllable of a weld as the gas counterpart. It's advantages are that it works well outside and you dont have to mess with a cylinder. The manual for the Millermatic 180 shows a flow rate of 20 - 30 CF an hour flow and I see where people say that they set their gauges at 20 and have good results. Divide that number buy the size of your bottle and that should be a good idea of how long the bottle should last. ( an 80 CF bottle @ 20 an hour = 4 hours welding time) I think I read that the miller has a solenoid in it so I'd guess that it only uses gas when you pull the trigger.
At my work all we run is miller, i learned to weld on several different brands including lincon but the miller seems to run nicer, but on the 220v models we have they all have preflows that you can program in it. If you want to skip on the gas bottles and the headache that can come with them give flux core a shot it can do most of the stuff that people are looking for in wire fed welding.