The big issue is the power supply needed to run an injection moulding machine. Even a small industrial machine generally takes 10kw, which although is only roughly 40A on a single phase supply, they're all three phase machines, and doesn't take into the account the surge of the motor(s) starting/stopping, so you really need somewhere with a proper 3phase supply.
Which pretty much means there's a very small market for old secondhand machines, and the prices reflect that.

I am hoping to buy one soon, but need to get a suitable power supply first!