ATI AT-94P, which is the pistol version, is the way I went. Accepts standard mags and takes standard stocks. You might be able to snag one on gunbroker for the old going price of ~1200 bucks, HKparts still had some in stock for ~1500; both are cheaper by several hundred vs the Vectors and other clones.
In rifle setup it's a very soft shooter, much softer than an UZI. The steel MKE mag (comes with a 30rd) works well but when locked in, with enough force, I can pull it out without hitting the release; need to hit the mag with a file to square the latch point. I bought a steel Korean mag and it locks in better, can't just pull it out, and has run just as well. I also tried a plastic MKE mag and they are horrible: thin plastic, rounds randomly pop out, bolt shaved pieces and turned the gun into a jam-o-matic.