Pistol caliber carbines in my collection include CZ Evo Scorpion pistol, Beretta Cx4 Storm 9mm, High Point 4595, Kel Tec Sub2k 9mm, and a 9mm AR carbine & pistol.

At an $800 price point a Scorpion or Storm won't be easy. They're well built and worth it. Not cheap. Both of these are surprisingly accurate with 9mm out to 50 yards, and the Scorpion is crazy quiet with 9mm subs. I see why they're a good host for suppressors.

Sub2k is an odd duck. Ergonomics aren't great, terrible trigger, mediocre accuracy. But VERY light & compact when open and the size of a laptop when folded. Irons are low and check weld isn't great. Easier to find but still usually selling for over MSRP.

My HP 4595 is my second HP carbine. I don't like their pistols but their carbines are great. Pretty simple, reliable, and overall compact with the magwell in the grip. Factory irons aren't great but they come off easily so plan to add a cheap optic. if you find one used they usually sell cheap but there's not much to go wrong with them, and HP has VERY good customer service, even if you're not the original owner. Hands down the cheapest pistol caliber carbine available.

9mm ARs like PSAs are cheap right now with complete uppers for $250-$300. I picked up a compete Glock lower for $170. Blowback ARs are heavy and don't manage recoil as well as some of these other carbines but they come with a GI single stage trigger that's better than any of these above and have a million aftermarket accessories. Also a good option if a 5.56 AR might be your next purchase.