score:4
I don't think there's a direct bus from Sao Paulo to Tiradentes.
Bus company Util provides several connections each day, most overnight, between Sao Paulo (Tiete) and Sao Joao del Rei, starting at 112 BRL and taking about nine hours. From there, you should be able to get a local bus to Tiradentes.
You might get lucky with a Blablacar, but don't count on it. And, keep in mind that there's a good chance the driver will not speak English.
(You could also fly to Belo Horizonte, and then get yourself to Tiradentes, but it's not likely this will be more convenient or cheap.)