Been shooting there the last couple months. So far they have the best price I've found around Indy, $6.50 for the whole day (6 hours to be exact)... Not sure what they mean $20 for weekdays. They are not open to public on weekdays...
I have worked as an RO at the Eagle Creek Range since 4/06 and the $20 is for just a one day pass. We sell 10 visit passes for $65. But the range is only open to the public on the weekends.