That price is far too expensive, look around.
If they leak, you can try cleaning them and see how you go. If the crack pressure is too low you can put shims in to increase the pressure. You say it leaks, you may just have a small piece of carbon stuck behind the needle of the injector.
The set i cleaned worked a treat, i pulled them down and threw them in my ultrasonic cleaner then blew down with air and re-assembled with a bit of diesel. I didn't have a tester for the crack pressure, i just hooked it up to an injector pump and cranked it over.
Don't use any metal objects if you do decide to clean them, use soft things like tooth picks or pieces of plastic.
Also, if the injector is leaking like you said, i assume it is dripping? so i hear that is really bad, it can cause pitting on the top of the piston. I don't know if thats just for direct injecton engines or not. Does it blow any sooty smoke when its running? it may just be as you said, a bad glow plug.
I'm sure you will get it sorted out!