Only worth it if your going to be keeping them anyway.Then a few bucks to feed the fish comes in handy.A shrimp tank is cool,if they are selling for that much,you got a customer,and think you would enjoy a tank full of shrimp,go for it.
If you collect used staples at work, your not going to be make a living from scrap metal.
If you cut the lawn every week and keep the grass, your not going to make millions selling compost.
What im trying to say is we get into it because for us its a hobby. We do it for fun. You cant go into something small scale and expect to turn much of a profit with anything in life, or everyone would do it and squeeze out any profit margins. If you want to make money from fish, its generally not fun anymore, it needs a lot of care and a lot of attention. Its a job. In my opinion make your money from something else, and enjoy your fish.
Agreed with the above posts, I'm not sure about rays I don't keep them but I do have experience with discus. Even then breeding them will only make some money not nearly enough. Importing them and selling them will.