While most insurance companies these days have some sort of co-pay, the actual amounts and for what do vary quite a bit from company to company, and even from policy to policy.

This makes shopping for insurance (I've had to pay my families insurance out of pocket while contracting or temporarily retired) a real headache inducing experience.

Generally the front office staff (not necessarily the nurses, but the folks behind the counter) have more experience with the billing and can assist you in determining the costs.