I got one of the standup cabinets from HDC tools for $99 for my truck parts, should be plunty big enough for AR stuff.
Just checked price is now 129 look on Homier.com 02763 Sandblast Cabinet
I use a black magma since the silica based sand is bad for your lungs (if your using it inside without a resperator). The black magma breaks down really fast and realy fine. I need to pull my cabinet apart and seal all the seams as it goes together then I'm going to attach a drop back filter (like a mufflers baffle to drop the big stuff back in and vaccum out the fine dust) that pulls through a good filtered shop vac. Then I'll be good to go.
it works though
homier also has a bench top cabinet also... 03091 Abrasive Blast Cabinet $49