want cheap, 200 dollar. find a garage sale cracker box. most time $50
+1.
If you just want to learn how to weld, this will be the cheapest route.
Look for a Lincoln AC-225 on craigslist or garage sales. Make sure the selector knob isn't twisted off, and the switch goes "kerchunk" to all positions. Otherwise there isn't much that goes wrong with these.
Pros:
Cheap!
Great practice for stick welding (later you'll want a larger DC welder).
Works great for 1/8" thickness and up.
Is capable of structural welds with proper skill
Cons:
Needs a 220volt/50amps dedicated circuit.
Won't work well for thin sheet metal.
Only welds steel (yeah there ARE aluminum rods, but I wouldn't expect good results)
Welds will have slag that needs to be cleaned
AC only (unless you find the AC/DC version, but that's more money)
Also you could look for a DC stick machine: idealarc, thunderbolt, dialarc, etc. These will probably sell for $500 or $600. If you buy the AC225 and you're serious about welding, you'll be upgrading to something else. The DC welder would be a 'keeper' machine.
A proper mig machine isn't going to be available in your budget. Expect to be in the $1000 ballpark for a good one.
As others have said, you CAN get away using a cheap mig machine. The cost of a good machine is usually worth it, if you plan on using it for several years to come.