Buy brand name Miller Hobart, Lincoln, etc, used on Craigslist if you cannot afford new. Definately get gas setup
X2! Get a gas set-up. Flux core works ok, but is sloppy and stinky. With some seat time, an inert gas (MIG) weld will look pro. You will be pleased with the finished weld and a lot less clean-up grinding. You should be able to find a used Miller, 110 volt with gas and stay within your budget. If you stick with a BRAND NAME you will always be able to get replacement parts and get it repaired.
I run an old (1980's) Lincoln Idealac 200 amp, 220 volt. $300 pawn shop score about 6 years ago. Every piece is still available to fix it and I have only had to replaced the liner in the stinger. This will be the only MIG welder I will ever buy.
I tell ya, new Millers have come down in price a ton in the last few years.
Check the link.
http://www.millerwelds.com/products/mig/product.php?model=M00234
Not quite twice what your budget is, But it will last you a life time!
JMO,
Larry