[Gav]

Baz,
HP tuners which is the software I have has a system where by when the software is purchased you can choose how many credits for different PCMs you require.
Some tuners will have a blanket purchase where they have unlimited access to a particular model PCM or multiple model PCM's.
You may assume that since you are a new customer each time, the tuner has charged a fee for the credits required to access your PCM. I would also assume that if you returned to either of these guys you would not be charged again as you have already paid for the access to your tune, the serial #'s for your PCM will be registered on their computer.

So no I would not think you are being ripped, but however if you continue swapping tuners you will continue being charged an access fee.