However, a couple things to keep in mind: First, you'll use up a LOT of gas. Depending on how much you cut and what kind of flow rate you set, I could see even a 50-lb tank only lasting a few days, or maybe only as much as a week.
Locally, CO2 is almost $2 a pound, so that's $100 in gas a week, assuming my rough seat-of-my-pants guess is close.
Then of course there's the hassle of having to keep swapping tanks, the requirement you have at least two on hand (one in use, one full backup, which often works out to being three on hand- one in use, one full backup, and an empty waiting to be exchanged) and having to keep moving around heavy tanks.
Second, also depending on flow rates, you can fairly easily "freeze" even a big tank. Sustained draw from the tank can cool it rapidly, potentially even to the point of freezing it solid- meaning little or no tank pressure, meaning little or no blast at the cutting point.
Neither of those things are unworkable, of course, or fatal to your idea. But should be kept in mind.
You can give it a try with a cheap 20-pounder (know anyone with a Kegerator? ) and a relatively inexpensive flowmeter. ($75-$100.) You'll probably want a flowmeter rather than just a regulator- the flowmeter has a reg built in, and does a better job of controlling the rate of gas flow.
A 20-pounder will also give you a better idea if you're going to get "freezing" issues- the smaller tank will freeze up a lot faster than the 50 or 100-pounders. If you don't have a significant problem with the 20, a 50 will work just fine.
And, as added protection, throw an inexpensive CO detector in the cutting room, down low. I'm pretty sure they also detect CO2, and should give you a warning if there's a leak or excess buildup.