DIY CO2 can seem cheap at the outset, but if you do the math, it's actually more expensive than pressurized after about a year, and DIY has a hard time generating enough CO2 (and doing it consistently) to handle anything bigger than about a 40 gallon tank. Lots of GWAPA folks that started out with DIY CO2 eventually end up going pressurized.
But it's awfully fun and cool to watch Chemistry and Biology in action!