Get a heap of 2 litre icecream buckets and put the males in them. Keep the baby females in a 100 litre plastic storage crate and grow them all up until they are similar sized to the ones at the petshop. Then contact your local petshop and ask if they want to buy any Bettas. Tell them you have 50 or however many you have for sale and see if they want them. Most petshops will buy fish for cash or store credit. You usually get less for cash (about 1/3 retail price) and about half retail price for credit. That will vary from store to store but it is typical around where I live.
If one shop says they will take 5 red and 5 blue then take 5 red and 5 blue to them and get some cash for them or get credit and grab some plants, fish food or another tank
Then ring a few more shops and see if they will take some.
Some shops will take large numbers but give you less because they are buying quantity. If you have 200 fish then try to find a shop that will take 200 of them.
Just make sure any fish you sell or trade are good quality and have 2 good eyes, full gill covers, nice fins and no missing parts. If the fish are deformed they should be destroyed to prevent the defect from passing on to future generations if they are bred.