Meesa,
You will pay an entry fee for each single-dance heat you do - somewhere between $25 - $35 per heat. Multi-dance heats such as championships and scholarships can range from $50 to $100 to enter. You will also need to buy your own admission ticket to the ballroom for each session you attend. Those costs are what the organizer charges. You usually can buy these either a la carte, or organizers very often put together packages that include meals, hotels and other things, depending on the competition.
As for what the pro charges on top of that: I've competed with a variety of pros, both chain and independent, and each one has a different fee structure:
-One charges a flat rate of $200 "per day" no matter how many heats I enter. So, if I'm there 2 days it's $400. He won't go to a competition unless there are at least 3 students going.
-One charges a "per competition" fee of $250 plus $10 per dance (so, if I've entered a 5-dance heat, that counts as five dances) Also, if I'm the only student going, his "per comp" fee increases to $300.
-One charges $25 "per dance." Again, if I'm in a five-dance heat, that counts as five dances.
On top of the pro fees, you will also expect to pay a share of your pros admission tickets, travel costs, and hotel that will be split among the number of students attending.
It does mean that you have to assemble the various pricing components and do a bit of math to see what you would pay for the number of entries you want to do, and whether a package is a better deal than a la carte.
If you don't want to do the math yourself, well, Chain studios usually will give you a single "all included" dollar amount to attend a competition that lumps together hotel, meals, entries, admissions, pro fees - but they quite often are very, very, very reluctant to break out the costs for you. Some people don't mind that; others do.