Seems to me that Teller wrote an OP a couple of decades ago noting that this could be done for much, much less than the costs proposed at the time for mitigation.
Here is a 2018 article from Nature saying:
“The process does not have to be wildly expensive; in a report last month, the Intergovernmental Panel on Climate Change suggested that a fleet of high-flying aircraft could deposit enough sulfur to offset roughly 1.5 °C of warming for around $1 billion to $10 billion per year.”
https://www.nature.com/articles/d41586-018-07533-4