If i'm understanding your proposal correctly, this wouldn't only be to sell bettas, but supplies as well right?
the problem with that is, that you would make the business deals with distributors to get products at wholesale prices, and then re-sell it to breeders like a middle man, which is no different then breeders buying from sites like aquabid or from the ibc website, cus lets face it .. even the middle man needs to take a cut to make some money. that's just basic business practices. even if your only making 1 cent off of reselling to other breeders, that is still a profit for you especially if your buying in bulk from wholesale. i know as a breeder myself, i go in with another breeder to buy at wholesale cost directly from a supplier. why would i buy from a middle man? unless you plan on selling the products not for profit for yourself and are willing to sell to breeders at the same wholesale price that you were able to negotiate.
also, since most established and serious breeders usually have their own website and sell their fish on their own site as well as utilize forums (classified sections) as well as putting their fish on aquabid (there are US breeders on there), and pre-plan with local fish stores etc. before they actually attempt to breed. Sure you will have your occasional breeder that produced a spawn just to "try it" and see what happens. but most of those spawns are given away, or sold for a very low price.
what many people don't understand when breeding is that even if your breeding pair are perfect, your spawn won't all be perfect. for example, from a 100 fry halfmoon spawn, you possibly might get 10-15% (could be more or less depending on the spawn) that are actually worth 20-50 dollars and are of breeding or show quality. usually breeders will pick 2-3 pairs to breed, and then some go up on aquabid, their own website to sell, etc. these do not go to mom or pop shops or lfs or pets stores since these are the cream of the crop. they are usually sold/traded to other breeders, entered into shows, which then after the show they are auctioned off at the show, etc.
then, the majority of the spawn would just be of the usual suspects that you see at local mom and pop shops (all the mom and pop stores around me hand pick the fish they want at their shop cus they know what their customers want and sells at their shop and what doesn't) that the store are selling for 6.99-8.99. which mean you sell to the store at 2-3 dollars per fish.
then you get the rest of the spawn that didn't get picked or sold. what do u do with them? give them away to family or friends. or take care of them yourself? these are usually the fish that end up at walmarts petsmarts petcos etc.
but i guess the bottom line i gotta ask from a business standpoint is. what will your site accomplish? why would i use ur site/service, when i can establish my own and not have to pay you royalties or a service fee or pay you to be the middle man? unless you plan on providing your site as a free service for breeders, then what's in it for you? we all know running a site is not free. how are you going to cover your over head costs?
it is a good idea, but there's a lot of other aspects that you haven't really touched upon that i hope you do cover when your business proposal is ready.
good luck! =)