Hey Alan,
I would try and push for warranty on this as it is a known problem and a Technical Service Bulletin (TSB) was issued for this fault (see link below - post #5 has the TSB info)
Noisey valves at startup - MPS 6, MPS 3 Gen I, CX7 2.3T
Also I had mine fixed at Wood Bros under warranty (1 week prior to expiring) so they have done the work and should know the price as dealers have to claim back warranty work through Mazda Aust. Service Manager is John Kenton ask for him directly, be polite but confident in your request when you talk to him.
Cheers
Chris
EDIT: Moved this to the VVT thread
Edit again: been 6 months and 10,000kms no more noise