To cut down on walking I would like to have a driver drop us and wait at several spots in Sofia for 4 hours. Does anyone know an independent driver who would do it for $20 per hour?
You might try contacting Lyuba Tours - https://lyuba.tours/about-us/ This company is based in Sofia and is managed by Stefan, Rick Steves’ fabulous guide in Bulgaria. They usually do longer tours, but maybe they can help you arrange a driver.
Sorry, I don't have any driver references. Although limited in scope, Sofia's subway system works as easily as those in other cities.