I got a Millermatic 175 off ebay for $640 with free shipping. They are all over ebay for a buy it now of $658 but i happened to catch this one as it was closing so I bid up to the $658 i would have payed for one of the others. And won.
Locally they tend to go for about $700
http://www.millerwelds.com/products/mig/millermatic_175/
I have used a friends 135 and another friends 175 the 175 was much nicer.
as i have hear the 210 is even better, But that was double the cost of the 175.
I also was considering the Hobart and Lincoln. Hobart does not have infinate adjustablity like the miller. And the lincoln was a little more expensive
here is a comparison of the welders i was looking at
http://www.millerwelds.com/products/mig/comparisons/millermatic_175.html
seemed to me the miller was best welder for the price
-Paul