A decent, engine driven welder (Miller or Lincoln, 6000w) starts at about $2500. (give or take, new price)
A decent 5kw genset (Homeowner grade) is less then $1000, and a stick welder is about $500.
How often do you need to weld away from power?
Engine driven welders tend to be designed for hard commercial use, and priced accordingly. You're probably spending more then you need to.