A new Auto Ordnance carbine lists for $777. Most of the old used ones will run what, 800 and up for a good shooter? Add 300 or more for a good optic and you're already to 1,100. Say 400 for a real nice optic, 100 for a mount, and another 100 for a new stock, add a modern sling, and you could easily have over 1,400 into your Carbine setup paying the going rates on your accessories. That's not counting any night time accessory. And sure, you could go much cheaper, but that's for the good stuff.
A really nice 40s production, refurbed Carbine, all by itself, is 1,199.95 at Fulton, for another example. Add an Aimpoint Micro (which is perfect for the Carbine, by the way) and the mount and you're up to around 1,800.00. Just depends on what floats your boat.