Hi. It depends on how much welding you do. I don't use much gas, since I mostly do gas-less welding. I own small tanks of oxygen, argon, and carbon dioxide. If you plan to do a lot of welding, the hassle of small tanks is not worth it. The welding shop near my home rents medium tanks for $4 per month and $120 refundable deposit. You can burn through a tank of oxygen in one heavy session, then you will be glad that you have the bigger tank. But, most of my cutting is with a hot chisel and a striker, or a saw. My little 40 cf oxygen lasts me 1-2 years. I picked this up for $60 on Craigslist. Do the math. This tank paid for itself in a little over a year. If you fill a lot, the rentals are worth it, since they cost less per cubic foot, and you have to go in less.
I have a buddy who used to weld a lot. He rented 2 large tanks. Then, he stopped welding for a few years, and put the tanks in a storage unit. He could have bought 3 sets of tanks new for what he paid in rental fees. Rent your first set of tanks and see how you like welding. But, make sure to return them as soon as you find out that you aren't using them. Also, keep an eye on Craigslist. Then, move fast.
I own a tiny argon tank which I bought on Craigslist for $20. It takes me a year to go through this thing, since I only use it to fix boo-boo's. I lent it to a neighbor who was migging a broken aluminum trailer. After going in to refill it several times in a few weeks, he figured that the rental was a better idea,
