Even at those prices for a tank, it rally isn't a lot of money. You will have the tank for your entire life. $160 spread out over 50 years. Pffft!
Same goes for a quality MIG welding rig. Sure, 1.5 k or so sounds like a lot, but it will be the only tool you will buy once. I've worn out 4 Port-a-band saws, 8 cordless drills and 3 welding helmets in the same 20+ years of owning my MIG welders.
I have had really poor luck searching the classafieds for used MIG units. In most cases the price is not much less than new or the things just get swooped up before I get a chance to buy them. Lots of times the ones for sale are the chinese knock offs. Good for small amounts of welding, but just don't have the robust build for something that will live in a pretty harsh environment.
I get people asking me to look over a welder that is for sale all the time. I just tell them to buy new. It will be less of a hassle.
had some refurbished Hobart units a while ago. I wouldn't even think twice. If they were the unit I wanted, I would buy them without heasitation.