If you're looking for gun taps, don't buy a set. Your typical set will be #4 through 1/2, and generally only course thread under #8. Gun screws are fine thread or extra fine, and #5-48 (not found in any set I've ever seen) is fairly common. You also won't likely find much use for the metric taps in a set working on guns. M3-.5 and M4-.7 are about the only metric sizes I've encountered on firearms, aside from muzzle threads.
Irwin or Vermont American HSS are as cheap as I'd go on taps. And personally, I hate using standard straight flute plug taps. I use mostly spiral flute taps, usually bottoming type, sometimes interrupted thread. Spiral flute taps are much better for chip clearing, especially in blind holes.
Whatever you use, be sure to keep from applying lateral pressure, use an appropriate cutting fluid, and clear chips as necessary for the tap profile and material you're threading. Exerting lateral force or binding up on chips is what breaks taps.
Dies? You'll really want adjustable type of high quality if you want threads to cut clean and straight. Solid hex dies are fine for chasing, but suck for cutting new threads. Be advised, getting a die to run perfectly true without a machine guiding it is really difficult.
If you're not in a hurry, I'd suggest cruising ebay and watching for good deals on high quality tooling.