We just paid a pest control $600 a few months ago to get rid of bats. One night we had a bat in our living room. We had no clue how it got in the house. My husband got the bat out and looked in the attic several times to see if any bats were roosting in there and saw nothing. About a week after that, we heard scratching in the wall. That did it for me, time to call in the professionals. I read on the internet that bats will come back to the same roost for years and their droppings have an odor that draw other bats to the roost, so I wasn't going to take any chances.....I wanted whatever it was out!
The pest control company didn't see any bats in the attic but said they can curl up and if there's only one or two, they can be hard to find. They did say there were a few bat droppings, but it wasn't bad. Our attic isn't the easiest to get into so we took their word for it. All they did was put "Bat Scat" in the attic and came back every few days to "fumigate". I'm not sure what they did the few times they came back to "fumigate". The purpose of the Bat Scat is that the bats don't like it and will leave. After a week or so, the pest control company sealed all the little cracks and crevices where bats can get it. Bats are like mice and can get into very small holes. We had a small opening where two roof lines meet on the house.
Here's a link to where they sell "Bat Scat". The exterminator said he put the bat scat in pantyhose and hung it from the rafters.
http://www.guardianpestcontrol.com/Bat_Control_supplies.htm
I'd try this and save the money that having a professional do it would cost.
Good luck!