Adding C02 is not always an easy thing to do and it is costly. IMO it is more cost effective to run th vented hoods. Unless you have a fully sealed room that you have environmentally controlled supplementing co2 is a waste of money. The equipment is not cheap, certain systems require tanks to be filled and hauled in and out of your grow and without being fully sealed you are just producing it in vain. From the sounds of your budget and plans you do not yet plan to build a full on sealed room and thus I would not consider co2 yet. The Lumens lost from the glass is negligible especially when you consider the benefits of pulling as much heat as you can from a grow. Even with vented hoods I have had tents hit 90+ degrees when it gets real hot out. I dont even want to think about how hot they would have gotten had I used wing reflectors. Even with co2 I think the recommended max temp is between 85 and 87. Without co2 its 80-82. So you gain the ability to be 5 degrees warmer without causing stress, which is great, but is not enough of a gain to make me go that route. Don't get me wrong I would love a fully sealed room running co2. The growth rates are usually phenomenal, you jjust have to have things dialed in to make it worth using.