Another good type of 'something from nothing' is to clone plants. Here is one example. My landlord let me bring this Plumeria tree up to my garden. Look down at dirt level - see those purple leaves hanging off the back left side? I moved that plant, let it grow, and now ~6 months later, have cloned it into about 20 different pots. This type of plant (Tradescantia zebrina, aka "inch plant" and "wandering Jew") grows quickly and is very easy to clone)
Starting the clones in jars of water:
See them on the bottom shelf here. Today that shelf is packed full. Now, I could clone about 30 new plants each month. (though I generally put 3 in each pot).
I'd like to start selling plants like this, but where I live, plant prices are low, so I doubt I will. There is more money in orchids, but I think they take much longer to clone.
Some of the plants in my garden, I have cloned by taking cuttings of plants that belong to my landlord. Some, I have cloned from plants around the city.