My colleagues put out an electric school bus market study and buyer's guide [0]. There are some examples of charging infrastructure costs on page 14 - looks like the high powered DCFC could range from ~$5k to ~$90k total. This isn't helpful for this Maryland instance, but you can see page 7 for an annotated map of where electric school buses are in the US right now, which includes Montgomery County, Maryland.
[0] https://www.wri.org/research/electric-school-bus-us-market-s...