I was wondering the same thing two months ago, that is, until my dance instructor told me how much it would cost.
I go to Fred Astaire studios, which I really like. The problem is, their competitions are at like 5 star hotels with all these luxuries and stuff. So you have the travel/food/hotel fee. Then you have the fee for every entry (I believe that was about $60/entry) and one would do an average of 20 entries per competition. In total it ends up costing about $3000, not including the price of gowns.
Yep, I'm not going to one of those until the day I win the lottery!!