Hi,........I can't think of any hobby that does not entail spending money to support it.........on a continuous basis.
I used to collect stamps when i was a teenager, mostly those that came on envelopes and were just the common variety until 50 years later those common stuff are making their way up the ladder.
If you want to have a hobby that drains every last cent........small bits of paper with glue on the back and a picture on the front are hard to beat for their size and value and the more imperfect they are the more they are sought after.
I personally consider CNC machining as a hobby.........when you have to do it continuously as a money earner it's not a hobby anymore and the machinery to do it must be top notch if you want to stay in business against the competition.
So which comes first......the product or the machine?.....it has to be the product of course......even a 3020 can make money if the product is suitable to it's light build.
Having a product would be something you designed and make that isn't bought, otherwise you're just an odd job man waiting for the world to knock on your door with a big order that you wish you had made/bought a bigger machine for............it can work, but the returns are in the lap of the gods.
A product that springs to mind is the common clothes peg.......everybody wants them, nobody owns the design patent and they are as repetitious as you need for a CNC run
That simple device made from 2 bits of wood and a weird spring device........I'd do away with the steel spring and fit an "O" ring over it......much cheaper than the steel spring.......just thinking outside of the box.
Ian.