all options are limited by $. A hand held band saw is great for lots of stuff, but is limited by the depth of cut, also a cold saw ( saw with a circular blade that cuts the steel not burns it away abraisivly) is a good way to go, but also limited by size of the blade, sears sells a grinder specialy fitted with two counter rotating blades that works as a cold saw. I havent used one of these, but the idea is great, the problem with cold saws is they spin at low rpm so they tend to catch and jerk alot if not used stationary with a vise. so by having two blades spining oposite directions it smooths out the operation. also a cutoff disk in a 4.5" grinder is pretty common. If your buying a grinder, the best one is the dewalt paddle switch. Much safer, because it wont stay on if you drop it after you cut your self because you werent wearing gloves. In fact I think all the on/off switch ones should be illegal.
There is also a "nibler" tool that works great for sheet metal, but is limited to very thin material... works kinda like sheers. Beyond these a sawzall can be very handy, and if you use a slower blade speed the blades will last much longer because they dont over heat.
HTH