Just in case you weren't talked out of it by Dave & Rose's posts...
Are you aware of everything you need? You need a large tank (like a 55) for all the female fry, and several hundred separate containers for the males. You need live food cultures to feed the fry--that is IF you can get a successful spawn without one of the bettas being killed, which can happen easily. You also need to be prepared to do Daily water changes on All of the male bettas' containers. If all that work does not phase you, then perhaps the moral issue will change your mind...it does not sound from your post that you have a pair of top quality bettas...so the fry you will be producing will be regular old pet store fish, and you will need to find homes for All of them. That usually involves begging the
LFS to take them, in which case they will probably not receive the best care...even if you find a store to take them that takes good care of their bettas, who knows what people will buy the fish & stick them in a bowl...
So, I really hope you decide not to. There are a lot of fish that are easier to breed & less risky to breed.