Actually they should do it for free.
If you paid in cash the deputy probably pocketed the cash. Call ahead and tell them why you want fingerprints and they will be glad to do it. We're the good guys making their jobs a little easier.
The deputy that taught my CHL class was pretty clear on the fact that here in Fort Bend County they are eager for more people to get their CHL. If law abiding citizens carry sooner or later in the right places, you know, like those cameras do.
Experience is a very bad teacher because it first gives you the test and then teaches you the lesson.