I already have scatterguns, that is actually my tool of choice.
Nope, going 5.56mm one of these days.
I built three piston driven ARs to test the three 'best' piston systems: Osprey, CMMG, and Adams Arms. It cost me right at $1000 each to build and another cash output to run 500 rounds through each. I'll sell one or two of them for around $900 each and transfer it to a local shop who can do the background and transfer, if you're interested. One of the guns is an 11.5 inch pistol version, tuned to run perfectly with the piston system. The other two are 16 inch guns and work flawlessly with IMI ammo or Wolf cheap stuff.
But you can build your own for around $775, with taxes and shipping for parts. of course, you will want a few specialty tools to work with, which will run you another $100 plus ...