Pablo332 - Cant say for sure what kind of cost comes from the technical support side of HUMS but I can say that I have personally never heard any grumbling or negative commentary in regards to the cost so I'm guessing it isn't bad. Having said that, compared to the euroHUMS/IHUMS (332 days, not 225, no experience with 225 HUMS) it does seem to behave much better from an operational stand point. Overall install seems to be much more reliable.
As for user hardware, it's really just the ground station ... Go to the local computer shop and buy a laptop with a PCMIA slot or card reader and off you go. Few hundred quid should do it.