A) You need to find a new mechanic, cause your current does not appear to be very knowledgeable if he/she jumps straight to the PCM...
I'm not saying that your PCM is
not at fault, however, the only way to tell is with proper diagnostics being run, which usually will identify the root cause, but not always...
B) As noted, PCM's are readily available, if you look around...
C) There are a number reasons for not starting, like the keys not being recognized, the ignition switch failing, certain relays/fuses needing to be replaced etc ect....
If your Expy has a passive anti-theft system (PATS), that can also be a potential point of malfunction/failure as well...
AND, as noted on the linked vendor page above, replacing the PCM is NOT a simple as removing the old one & installing the new one.. they have to be programmed to your specific vehicle
during installation, using the VIN number, so that all applicable codes & programming is correct and as current as possible...
Anyways, good luck & please post back with your results