You need to do some more research; you should not only not be breeding fry without a heater, you shouldn't even have bettas without a heater. Also, as everyone mentioned, have you read up on it? Do you realize how many babies you'll have if you suceed? Do you have tanks for all these offspring? Can you afford special foods, medications, etc. for the growing fry? Where/how do you plan on selling all of them? Plus about a billion other questions. I'm finding that with any species - dogs, cats, rabbits, and yes, fish, "backyard breeding" is causing a lot of unnecesarry death and suffering to the animals involved; breeding should be left to the professionals, not any person who can throw a male and a female together.
What kind of bettas do you have anyways? Because if they are VTs, they aren't going to be easy to sell seeing how mass-produced they are right now.