If you're going to buy an airplane with a potentially affected engine, I'd certainly make sure I had an extra $10k sitting around to comply in the event an AD comes out that has timeframes in-line with the service bulletin (100hrs/12 years in service). While that may not be how an eventual AD reads, it might be exactly how it reads. Replacing that gear requires removing the engine from the airframe ($$$ in labor), disassembling it ($$$ in labor), replacing the $1200 gear, potentially machining the case to make it fit ($$$), reassembling the engine (which will require quite a few $$ in consumable parts that can't be reused), and reinstalling the engine on the airplane.
I've seen shops quote ~$6,000 for a teardown inspection of an engine; that's probably the starting point for this + the cam gear. Combine that with the labor to remove and reinstall the engine, you're at $10k quickly. Making matters worse, some of the affected engines will ALSO have non-VAR cranks in them, meaning when the engine is split the crank has to be replaced (~$4-5k for a used one) per another AD. So all of a sudden, you're at $15k+ to comply. ****ty situation all around. Double ****ty for Baron owners.