Are you going to keep fish in it too? Read a little closer about how the sugar/yeast fermentation can make the pH fluctuate dramatically.
One diffusion method is to run the airline tubing in the intake of a canister filter. Pros: CO2 almost completely dissolves in the water. Cons: some canisters won't operate to full potential (fluvals) and it will make lots of noise. I've read that some Eheim canisters are used for this method successfully.
The other method is using
this or
that.
My facts might be off, I've just recently been researching CO2 injection. I've ruled out the DIY because it seems that you have to constantly keep an eye on pH levels and change the sugar/yeast concoction on a regular. Now I'm just looking for the cheapest yet effective CO2 injection unit.