Most places I know will negotiate a discount for 50+ bettas. I say your best bet is to go on Aquabid.com, contact a few sellers there, and explain you need to know for a school assignment. I have a feeling most will be kind enough to offer you a rough quote.
yeah what Stone said because I have an entrepreneur class and in that class we need to make up a business so i chose to have a pet shop. I just wanted to know how much it will cost to buy 50 male bettas from a wholesaler because I need a resaler's license to know how much it'll cost me to buy it, and I also need to sell it for an exact price in order to give me a profit. So i'm not actually going to buy it, just wanted to know how much it'll cost.