Around here, it really depends on the county.  Westmoreland and Cambria counties, for example, don't charge for their index printouts; most other counties here in southwestern PA charge the same per-page rate as they do for regular copies.

I generally don't copy indices in the counties that do charge, except in a case where I find a glaring error in a particular index, in which case I'd get a copy of it (to cover my a**) before I bring the error to the clerk's attention and another after the error is corrected.

Hope this helps.

Regards,
Scott Perry