There are various 26mm (one inch) euro-military surplus flare guns around in the $30-$40 dollar range, google would find them for you quickly. I have a couple, some German, some Polish, all basically the same and all built like tanks. Many will come with carry pouches that can carry several flares as well.
The only drawback is that they are all made at least partially of blued steel and will rust if not cared for.
Personally, I'd suggested starting with the flares and working backwards from there. Do you need special colors or a particular caliber? Is fire safety an issue? Don't get one of these guns unless military surplus 26mm flares will do what you need them to do.
Another option is a just generic 12 gauge and a box of 12 gauge flare rounds.