If your good with the welder, just fix the hole. These tanks don't "explode" like some people imply. They just don't know any better and compressed air scares them. If there is a rust hole, obviously the thing didn't "expode" or rip apart taking out half the barn.
If your metal savvy, just cut out a nice little square, circle or triangle for all I care, but be sure you cut clear of the pitted rust area so you can get a nice solid penetrating weld.
Also, use some nice thick gauge steel. The thicker the better. Don't expect to patch this thing with some 22 gauge. Use something thick like 16-18.
Rust does not weld, it melts, so if you start burning holes in the thing, you didn't cut far enough.
Hopefully the tank isn't too far gone and is repairable. If not, THEN go out and get another tank.
Otherwise, save your wallet, have some fun. Use your head, be smart about it... and if your not up to the job, just don't do it. Or have a buddy do it. The worst I could see happening is having it leak again. Big deal.
If you do fix it, then you will have 1 more tool you can point at and say... "I fixed that".
Much more rewarding than.. "I bought that".