Part 1 - Greenhouse Gasses!
Lets go with Sulfur Hexafluoride. On Alibaba you can purchase SF6 for about 10$ per kilogram from china. With a molecular weight of 146 grams/mole this would work out to 6.85 moles, which is about 153 liters. Let's see what our money can buy, at 10$ per kilo thats 100,000,000 kilos of SF6. Now SF6 has global warming potential of about 16300 times carbon dioxide, so let's call it equivalent to 2.12 X 10^14 kilos of CO2.
Now this seems like large amount, but it is actually not as significant as you could hope. This would only increase the amount of carbon dioxide (equivalent minus other gasses) in the atmosphere to 3.37 X 10^15 from 3.16 X 10^15. It is significant, but would only accelerate global warming by about 40 years. We need to get more efficient, obviously just buying this from some no name supplier in china is not effective. So we need sulfur and fluorine. Sulfur is easy, just get it from Fort McMurray, AB. They have way too much already from the refining of heavy oils.
This pile alone is way more than we need, and could be obtained for
pennies per kg. Now the fluorine is more expensive and harder to find, but there are many mines and it can be obtained for about 0.20 $ per kilo commercially, probably about 0.10$ per kilo (or less) once we own the mine. So let's estimate our costs for materials at about 0.08$ per kilo. Production will cost much less than other producers, since we don't need to bottle the gas or ship it anywhere. On a massive scale let's call production costs 0.42$ per kilo (because round numbers are nice). This brings the total cost per kilo to 0.50$. This is an increase of efficiency in the order of 2000%. It will do.
New CO2 equivalent 4.24 X 10^15 kg. This brings up the total CO2 equivalency in the atmosphere to 7.4 X 10^15 kg, Very Significant!
Hooray! The world is ruined!