We have found very few PCM Power Train Control Modules = ECM go bad on the Crossfire. There is more likely a problem somewhere else. It would help us, help you if you can tell us exactly which diagnostic codes your car is setting. Give us the exact numbers; NOT some wordy explanation from a mechanic.
Why did you bring the car in for repairs initially? As to the parts you may need, some are available from online retailers and others will need to come from a wreaked car; depends on the part.
You say a "Qualified Crossfire" mechanic. If that means your car is at a Chrysler dealership you should get it out of there. Even if they have the old diagnostic equipment (The new scanners at Chrysler dealerships will not work on a Crossfire) to scan your car any repair will be much too expensive compared to other specialized European import garages.
Get the numbered codes; tell us what they are.