Lots of variables. Room size, budget, number of plants, how many watts/type of lighting. Show some pics of your op and we can help you out better. Do you know if you want to go with a generator or a tank?
Judging by your space in the pictures an Exhale bag or 2 would suit you just fine. Propane, Natural Gas, and compressed co2 are all costly and are an option for professional gardeners with a larger room. - Exhale bags contain mycelia that produce co2 through their natural processes. ExHale CO2 Bags -Excello Fizz from supernatural are convenient pucks you can use also to produce co2. Excellofizz CO2 Pucks -Also baking soda and vinegar create co2 when added together. Harnessed correctly could provide a co2 source Keep the method of co2 generation at a higher elevation than your plants so the heavier co2 gas rains down evenly upon your plants. Although, I have no experience with ExcelloFizz, I sell quite a bit of exhale bags to customers at the hydro shop I work at. Most methods of co2 generation are quite expensive to maintain often creating unsavory byproducts like heat when using a co2 generator with either propane or natural gas. Co2 tanks are expensive, and need to be replaced often. Quite heavy, and not fun to carry to swap for a refill.
^^^All correct. For the $$ and your small grow space you could just use the pucks or a simple fermenting style source. As a devils advocate, I also should say that Co2 tanks aren't really any work if you have a regulator on them. For your space you could get a 5 or 10 pound tank for under $50, but the regulators are about $100. I completely agree with the above posts, for the money and how little you will need I would just get one of the puck or liquid generators which you can either get at a hydro shop, build yourself, or pickup off ebay for pretty cheap.