I would say a completely PRO Co2 setup shouldn't cost you more than $250
Get a Co2 tank at a local welding supply place, they normally run around 100$ filled the first time, and then it's yours to keep. And you can get a Co2 kit with everything you need here
Co2 Kit including regulator, flow meter, solenoid, pressure gauge, plastic dispensing tube, instructions and timer. Great deal I'd say.
Course you could always spend a fortune on yeast packets and mix yeast water and sugar in a jug everyday but for the amount you get it's not really worth it.