I paid $300 for an injector pump in 2002. It's functioned in the 70K miles I've put on the truck since installing it, but I question the build quality. The fuel shutoff solenoid and timing advance solenoids have a nasty habit of sticking "ON", and even with the timing properly set, I feel that the engine's down on power compared to where it was with the old pump.
Is that the average experience with a $300 injector pump? I can't say for sure, but after dealing with that pump, I would strongly recommend getting a pump from a rebuilder you know and trust (Mel, Russ, etc) before getting one from eBay.
Just my $.02...