the bigger amp the better the welder is generally, a 150 amp welder is probably a good one to go for for thin metals, although a bigger amp welder will weld tidier and get more heat through. id say you would get a half tidy one for around the 200 mark second hand. stay away from the sip welders though, they are not very good, clarke and sealey i have found ok, the best welders always seem to be the big amp ancient ones!!!