In reply to Enty:
If you want cheaper ones, have a look at boating supplies - you should be able to pick up captive SS karabiners pretty cheaply, and maillons to install them too.
That being said, i would question why you want to install a screwgate permanently? They don't really last any time at all before seizing shut, and then you just have a badly made threadable ring which some poor sod has to angle grind to get off again.
From a maintenance perspective, it is far nice if you either use rings, or at the very most, non locking karabiners.