Live in the desert and had a swamp cooler in the shop for several years. Very dry here (understatement), so it was good for up to about 94-95 degrees, after that it lost the battle with the heat, despite the insulation. I kept all steel surfaces coated with paste wax, so I didn't have much rust problem. Much happier with AC, although it costs more to run it, it has the advantage of cooling things down faster, and as soon as I finish working, off it goes. Cost is slightly more for an AC in a small size, but by the time you mess with running water to the unit, it comes out even on initial cost. We have freezing winters, and the copper or PVC pipes were always bursting, wrapped or not. In a larger size, the AC is going to cost more. But the newer AC units are more energy efficient. I don't mind a little heat, so I set the AC to about 74 degrees, so it doesn't run constantly.
Last thing, with the swamp cooler, you MUST have a vent to let the moist air out, otherwise you'll get condensation and reduce the cooling effect. I just kept a window or two open in my small shop.
That's my Southwest swamp cooler experience--just go to AC in my opinion, and only run it when you're in there.