I made this DIY homemade CO2 generator by following the instructions on this website:
I filmed this video right after I set it up for the first time, and a couple hours later it was producing even more CO2. It uses yeast, sugar, and water to produce CO2 for aquarium plants, and it cost just a few dollars to make! Within a couple of hours of taking this video, I was able to see pearling on my plants for the first time!