With no money outlay you can collect seeds for free, collect soil for free and plant in second hand wax cartons or plastic bottles recycled from your kitchen. Taking cuttings from existing plants is also an option for making more plants for no more money.
This is my current personal tree growing project to plant out as many small fruit trees back into the jungle here in Costa Rica for the good of locals and animals alike.
Within months you will have plants big enough to sell on though - or if you don't need the cash just grow and plant out in your area. The world always needs more trees and flowers .
Happy gardening!