Make that 100 billion more. There are ways to develop this, much like trying to figure out meteor impacts by using railguns. Effective scale models of Earth ecosystems are darn hard though, as we found out in the handful of "biosphere" experiments.
Expensive hardware required, lots of capital investment, easy to miss something and mess up. If NASA cannot do it, your rinky dink startup probably cannot even more so, though we still need to try. And NASA is also effectively underfunded plus has slightly different goals than terraforming Earth.
We could use like half of the oil dig and weapons budget plus expert manpower to actually devise some actual quick and effective policy solutions to the hot mess grandpa and dad dealt us.
If pumping SO2 into the atmosphere becomes profitable via cooling offsets, we might struggle to get people to stop doing it.
Industrial scale CO2 and SO2 production might be how you get to Venus.
And "the economy" is fighting to keep the climate change going to the last breath, because taking any tool from the chest (and we have an overflowing chest right now!) that is effective and working would 'hurt the economy'.