Does it cost anything, once you pay for the marriage license, to get married in the courthouse?

Varies by court, the clerk where you get the license will tellyou, and tell you what times during the day they will do the weddings.
Some do it as you wait to the first available judge, in other places, like our courty here they do it twice a day, and you stand in line with the others wanting to be married at that time.

Also many clerks have a list of pastors that will do weddings in your home, or even at the court hosue