Best and the cheapest I've found is a Craftsman 4 1/2" electric hand grinder with 4 1/2 cutting blade installed (I get mine at Home Depot, $1.98ea).
More power and cutting adlity than an air tool and less punishing than a sawsall.


1959 Shortbed stepside 1/2 ton project
[Linked Image from i236.photobucket.com]
[Linked Image from i236.photobucket.com]