Oh right, I forgot they cannot be automatic, is that right? Sorry I live in Europe where all sorts of arms are illegal... automatic, short barrel, long barrel... pop guns (see UK)
And yet $1600 (imagining that the rest of the parts are free although they are not) seems to be near the level of high quality replicas.
Perhaps with some luck a $2000 version could be possible, laws allowing it.
What about blank firing ones?? Those will do the trick too (and they would be screen accurate) ... gee even cap firing ones would be great to see in action! (better than the new sound and lights system they use at Alien Wars this year!)
From model-guns website a Thompson is about $600-700, shotguns are around the same price. They are quite loud too. I'm surprised no one has tried it yet.
I simply don't have time, money, skills or enough interest to actually try it myself... but I'm surely dying to see something like that happening ... and see some videos of it on youtube