The most common symptom of a bad oil pump is low oil pressure.
Your oil pump is supposed to produce between 45 to 55 PSI in oil pressure when you accelerate and at idle as well.
If you notice your oil pressure is not going up when you accelerate then the oil pump is likely bad or your oil filter could also be clogged or you have low oil level in the engine.
Check to make sure your engine oil level is up to the proper level and make sure you've changed the oil filter as well.
In some rare cases when an oil pump is severely worn out or damaged it may make noises such as whining or whirring noises as well.
Most oil pumps will last the life of the engine or car and usually do not need replaced but if it does go bad then replacing it will require dropping the oil pan and then replacing the oil pump and then putting the oil pan back on.
The job can cost from $200.00 to $500.00 depending on the shop that does the job and how long it takes them to replace it.