Where I live, I can do an amateur collegiate comp as an adult non-student for $20 per person. I can do a USA Dance amateur comp for $15-$25 per person, depending on if it's an unrecognized (i.e., non-point-granting) small "club" competition or if it's a big Regionals. Hotel-based NDCA comps run between $60-$140 per couple, depending on how many events we enter, and how many different sessions they are in.
Back when I was doing Pro/Am, entries ranged from $25-$55 per dance for the single-dance events, and from $75-$125 for the multi-dance events (like the scholarships). We'd get halfway decent money for the scholarships, too, like first place would be $500, and the checks were made out to the students. Ticket prices (because they are pretty much never included in the entry fees out here) ranged from $15-$45, depending on the session. Obviously they put the more prestigious events, like Amateur Championship Standard, in a more prestigious (and expensive) session, like Saturday night. The syllabus and novice dancers usually get scheduled in the afternoon, when tickets are cheaper.
The big question marks in Pro/Am pricing are (1) the fee to dance with your teacher and (2) any studio mark-up over the organizer's prices. When I started with my teacher, he charged $20 or $25 per dance, I can't recall. Six years later, when I stopped, he was charging $40 per dance. Some teachers charge a flat fee. Others charge on a sliding scale (the more you enter, the less they charge per dance). The fee to dance with your teacher is a very individual thing, it varies from teacher to teacher. As for the studio mark-up, my teacher was an independent and so the studio never came into it, so there was never any mark-up. I've heard horror stories of massive studio mark-ups, and I think that those are ludicrous and give Pro/Am a bad name.