You must be with a chain studio because they control the money and pay the pro. All comps post their entry forms on their websites so I presume you are talking about an in-house comp run by your studio chain.
I usually sit down with my instructor and we fill out the form together only because I cap how much I will pay. So we figure out how I can get the most bang for my buck. We figure out how many single dances, championships etc., I can fit into my budget. I pay exactly what the comp is asking. Anything else, is itemized by my pro and a bill is given to me afterwards. There are no hidden fees, no misc. extras. I have always been very up front about what I will pay for and how much. It is a conversation every student should have with their pro/studio but many students don't want to look cheap or make their pro/studio angry so they don't talk. You should know exactly how much extra they are charging you and how they came to that amount. Do they charge by the dance, by the day? Studios pay the pro very little and keep the lion's share for themselves. I believe pro-am fees should be completely transparent. Keep asking questions, it is your right.