When a rod bearing in an engine is going out you'll usually hear a knocking noise when the engine is starting up or when it's idling.
Then eventually you'll hear usually a squealing noise which gets louder and louder and the longer you run the engine like that with the bad rod bearing the more damage the crankshaft will suffer.
Eventually your engine will seize up and fail to turn over again.
Then once the engine rod bearings go out you'll need to have the engine pan dropped and then have the engine rod and main bearings replaced.
That can be costly if you hire a shop to do the job of replacing the rod bearings.
Sometimes it's easier and cheaper to just replace the engine or the vehicle with a different one.
I've replaced rod and main bearings myself for $40.00 in parts for the bearings and then another $20.00 for the oil pan gasket so I spent around $65.00 in parts for the main and rod bearing replacement.
But if I were to hire a shop to do the job it would cost around $500.00 to $1,000.00 for the rod bearing and main bearing replacement.