My original post said ~$50-$100 in initial setup, so you're not being fair to my original post. You need multiples of the things or similarly functioning things as posted. Yes, buying bigger bags of dirt is an option, or cheap plastic pots. If you're going to be doing this, you'll appreciate the clay pots as they don't bet brittle from UV exposure. I prefer clay as I just dislike plastic.
It's a typical reaction when suggestions that gardening can be more expensive than people realize. Yes, if you use the same pots, start taking seeds generationally, etc the price amortizes to near $0. That first year though can put a dent in a wallet. If you've been doing it for awhile, it's easy to forget.
We haven't even discussed getting into drip irrigation or similar. Each of the individual parts are cheap (tubing, sprayers/drippers, etc), but again it adds up with a timer etc.
To be abundantly clear, I'm not trying to dissuade anyone, but just giving realistic expectations. It's just like getting into Arduino and what not. The controller itself is cheap. The shields are cheap. Electronic components are cheap. Then you add up all your receipts and realize, you've spent more money than originally anticipated. It's just the nature of DIY.