Some plants that you could grow for big profits are plants like Hydrocotyle tripartita that at the fish store sells for $7-10 and just a tiny 3-4 sprigs rooted in rockwool. I put mine in a jar outdoors and its growing pretty well considering its February. Easy and fast grower in or out of water I bet. Same for Monte Carlo,Hygrophila pinnatifida as expensive to buy and grow fast out of water.
Others like Anubias? I see as really slow growers but I saw Anubias nana at a store for $10 and it was just like three leaves..3 small leaves for that price. If you can get them up in production,they always sell.
One big profit maker if you have Co2 is Bolbitis. That plant is always in the $20 range and then add shipping to hobbyists who want one. Get it on Co2 and the lighting does not have to be anything special. That's the crazy thing about that fern. But,it is very sensitive to low Co2 in the average aquarium and that's where it starts to die off. I don't have CO2- but I do aim pump water at it and use the vortex of a powerhead and that has helped. You get that growing thick and you can retire.