JM, If a mandatory inspection ( or some other fault) has been missed by your previous maintenance org then go back to them to sort out the issue, I am sure they will be willing to explain/justify or compensate. If you still don't get satisfaction phone the local CAA SRG area office and discuss it with a surveyor.
Blueskis, looking inside an engine, especially a high time or low utilisation rate, will reveal corrosion, worn cam lobes, general wear outside of rebuild limits, internal leaks etc etc - none of these will noticeably affect the engine operation.
Our company is ISO 9000, IIP etc etc but the houly rate is about £45 per hour - most M3 orgs are not hence an houly rate of £20-30. You get what you pay for.
My advice to anyone is to: -
a) Shop around and get at least 3 quotes.
b) Get a personal recommendation from someone who is happy with the organisations quality of work and value for money.
c) All the information regarding AD's SB's for the engine and airframe are on the CAA and FAA websites, check them out for yourself.
d) If you think you are being ripped off or are likely to spend a large amount of money, employ the services of an independent engineer to check the details.