I mean one reason methane is worse is because it also becomes co2 but if we got a handle on the co2 we would not be in so problematic a situation. that being said there is about twice as much co2 in the atmosphere as pre-industrially and its at 500 billion metric tons. the cost was 1k per metric ton. a thousand billion is a trillion so it would cost about 250 trillion dollars to get us back to pre-industrial just for co2. if it actually ends up being that cheap. world gdp is estimated at 100 trillion and of course humanity is made of very selfless folks at the wealthiest levels who are way ok with sacrificing their wealth for the good of the planet /s. As you point out that will not get rid of methane or any other pollution we have in the land, water, and air.