There are some relatively cheap co2 systems out there. (
http://upaqua.net/products/co2-systems/pierce-co2-starter-package/)
You can do the diy co2. Or you can try to grow the grass without it. If you dose Flourish Plant food you might be able to get away without having co2.
I would recommend trying flourish tabs in the soil to create nutrient rich soil, and dosing the liquid flourish plant food once or twice a week. See how that goes before you buy any co2 system. Co2 is not always necessary if you have lots of nutrients that the plants can feed on.