I would buy something high quality
Miller is the best , Hobart or Lincoln are good , probably 110 powered , 220 is preferable but you need to make an extension cord from you dryer plug or wire a new plug into the panel
a mig with gas capabilities is a must , huge amperage is not an issue with body work welding .
Grainger had a killer deal on Miller last month , that have an auto feed setting so you set the heat & it will feed in the correct wire speed .
the typical dollie I have seen bolts to the front spring hanger mount , you can build a bridge to bolt onto the K frame holes in front .