Greg,
Check into leasing the tank from your gas supplier. It's usually cheaper and they will upgrade to a bigger tank quite reasonably. The probelm with owning the tank is once it reaches its service life it will need to be re-certified, tested, and that comes out of your pocket.
I'm only assuming your supplier has the lease option. Mine does. I lease my argon and C-25 tanks. Refills are cheap too. Under $100. and I have the big tanks.
Funny story: I was leasing a big argon. I'd had the lease for 20 years, had it refilled quite a few times, then one day I got a check in the mail from my gas supplier. It was a refund for my lease fee. The state of Colorado has a clause that says anything leased for 20 years automatically becomes the property of the leasee and the one leasing must refund the initial amount. Now the tank is mine and my gas supplier refills it, no questions asked. It has a long time before it needs to be tested so I'm good.
Nothing like getting something for free. Too bad I didn't get some interest on my lease fee. 20 years at say, 5%?
Tom