Rates differ depending on size, desired amount of detail, and opportunity for sale as a digital print.
They typically end up between $2 and $5 per square inch.
Logos start $350, which include 3 iterations of design from sketch to final and delivery of digital files (thumbnail, medium, and large sizes with transparent backgrounds)
Variations or other specifics may add to the cost.
Other digital commissions are priced by the project, depending on detail, necessary design consultation, and other factors.