The US Embassy has a list of places where you can get tested, so you can compare prices: https://jp.usembassy.gov/services/pc...ties-in-japan/

These places may or may not be publishing their prices. Some places may not be able to serve asymptomatic patients and then there's the language barrier.

Rapid tests are just as valid, though. Either track one down through your health department or get it through your airline. I know UA has that option.