FWIW I know someone with a Kahr M1 Carbine that runs fantastic and is super accurate. They sell new for $650-700, I bet you could find a used one for around $500. That's really not a bad deal, but I don't see them as much of an investment since they make more every day. Having said that, I paid $900 for my Korean War era refurb that probably hadn't been shot between the refurb and the time I bought, as the park on the bolt was undisturbed whereas after probably 700+ rounds in the last year it's worn to be like a lot of others I've seen. It also came with 2 USGI 15 round mags, an authentic sling and mag pouch, a USGI 30 round, and 150 or so rounds of new ammo.
One of the best purchases I ever made, I put a new USGI recoil spring in and replaced the 15 round mag springs and it runs great. Super cheap and easy to load for too, my load with H110 and Armscor bullets run around $.19/rd. Supply has pretty much dried up, so what's out there will only go up in value unless you trash it. Downside is that also means no more cheap surplus ammo and it's a bit pricey to buy new ammo. At any rate the less expensive ones will be mix master refurbs but that's okay, especially if all you need is a shooter.