No you can't sell betta fish eggs and you cannot sell them right after they hatch.
Have you done any research at all? Start here
.. read EVERY article she has under breeding bettas and raising spawns. Also read the sticky in the breeding forum. Then go through the threads under the breeding forum... there is a lot of information out there.
You are not ready to breed. You need to understand what goes into breeding before even thinking about breeding. I know you're young but please listen.. this is not a joke.. this is very serious. Your taking lives into your hands... you have to be ready, you HAVE to know how to do this the right way.
I've been researching for over a year on how to breed bettas.. a YEAR. I started collecting stuff for my spawns over a month ago and I still haven't spawned. I've carefully planned out each and every step making sure I knew what I was doing and what I wanted from the spawn.
"Research until your brain hurts"..
How do you harvest brine shrimp?
What do you feed fry at various life stages (1 week,2 weeks, 1 month..)?
When should you remove the female from the spawning tank?
When should you remove the male from the spawning tank?
What is the #1 most important thing to have in raising fry (or keeping fish in general)?
What is culling and how do you do it?
At what time do you start jarring fry?
What do you do if a sickness emerges in the grow out tank?
What foods should you feed to condition your breeders and how long should you condition them?
WHAT ARE YOUR BREEDING GOALS???
Before you begin to breed you need to be able to answer all of these questions and more.