The California Air Resources Board has published a downloadable macro-enabled worksheet tool for estimating electricity costs for electric bus deployments. Transit agencies considering purchases of e-buses can use the spreadsheet to calculate their cost savings.
The tool estimates monthly electricity costs for e-buses that are charged at the depot or en route. It allows numerous variables to be factored in for the 9 California utilities that are included. It uses current utility rate structures, but will be periodically updated.
While the calculator is aimed at California transit agencies, it could presumably be modified for use by fleet operators in other regions.
Source: CARB via Green Car Congress