FWIW, I would take a serious look at an Eastwood like this one:
http://www.eastwood.com/mig-175-welder-cart-and-helmet-kit.html . I have this one for my garage welder. I did a review here:
Eastwood 175 Mig Welder (240v) Review
I've been very happy with it. Especially for the price. Great for a DIY home welder. Has enough power to weld pretty much all of your auto related stuff. Not big enough for production work (only 30% duty cycle), but works great for me.
And to give you some perspective my family owns a metal fab shop so I have a pretty good idea of how it compares to both Miller 250 amp and 400 amp machines. It's not as smooth or quite as powerful as either larger size, but the reality is that 99% of the use of the larger machines is under 175 amps.
For the price it's an excellent little 240v welder. And it comes with a spool gun - albeit a kinda crappy one - but functional and very nice to have if you need to do a little bit of aluminum or stainless welding.
I would not buy the smaller size to save room. The reality is that you'll end up with a cart and tank and the size is about the same as a midsized 250 amp machine.
Of the midsized machines, having used Miller, Lincoln, Esab, and Panasonic, I believe that Esab makes the best. They are not as easy to find or get parts for, but I would buy an Esab for my shop if I had the need for a larger welder and price was comparable. Not to say the others are bad, but that's my preference. The only one I would not buy of the above is a Panasonic.
The best way to find a cylinder of gas for cheap is to buy used. Make sure it is owned not leased. The owned ones will be stamped on top near the valve. You can google how to identify them. You can usually buy any type of compressed gas cylinder and trade it for what you need. I bought an empty acetylene tank for $50 and traded it for a full c25 tank and Praxair only charged for the gas refill and a pretty cheap tank swap fee. A lot less than the $200+ for the cylinder. My family's shop leases large tanks because it's cheaper for how many they keep and use - and they use the larger sizes.
Good luck.