Keltech sub 2000 (multiple pistol mags including Glock)
Beretta CX4 Storm (Beretta mags)
JP GMR-13 (Glock Mags)
SIG MPX (proprietary mags)
The Keltech is cheap and it looks the part. But they work.
The Beretta has an advantage for left handed users as the bolt it reversible.
The JP is AR platform with a custom lower to fit the Glock magazine instead of the more common magwel adapter. It is blowback operated like the Colt and clone styles.
The MPX shares many AR parts like the trigger, grip, and safety. It is gas operated. The magazines are $50-60 each.
With the PCC class coming into some of the competitions the JP and the MPX are popular choices. You are then getting into $1400-1500.
I'm building a SBR from a SIG MPX pistol host. It is a pretty fun gun to shoot as a pistol. Hopefully my form 1 will be approved so I can attach a stock to it soon.