If you have a need to weld both sheet metal and bigger stuff on a budget don't be afraid of two used machines.
Small migs don't cost much, carry like a duffel bag, use small wire set up for thin stuff. Remember if you go MIg you will need flux wire to be out in the breeze.
Do not underestimate the convenience of welding lead length on a stick welder, vs having to get your mig close to what you are working on.
AC stick welders are very inexpensive and will do most anything you want if you practice.