Wow. Laura hit the nail right on the head. The only additions that I would make...
Many independent teachers will actually let you see the packet sent to them by the competition organizers. This is sometimes thought of as a big no-no...but I know many independents who are this honest with their students. Given this info you can determine exactly where your money is going...and I personally feel that all students should know what they are paying for down to the last dime.
Your a college student? Check out your local universities and see if any of them offer a ballroom club. Colleges have the option of competing in the YCN (Youth and College network) events. These events are VERY LOW COST, and feature all collegiate participants. Besides, you may find an amateur partner that way!
Finally...buy a used dress! There are lots of great sites on line to shop...but be sure that you know what you are looking for. You don't want to spend $400 and end up in a knee length standard gown with feathers (circa 1980). Dress is important! At a beginner level you may be able to get away with something found at the mall and altered....it just depends on your level.
I have seen too many good talented dancers quit this sport because of the expense involved to compete! Pro-am is IMHO the absolute best way to learn how to be a good dancer in the beginning. That said...dancing with an amateur partner is alot cheaper...dancing with an amateur partner through the YCN is cheaper still!
Email me if you need to know what colleges in your area are YCN affiliates.

championdancesport@comcast.net