Hi,
We noticed that the Nori Bus from Takayama city to Shirakawa go costs about 4,470JPY (return). We found a car rental agency that that actually costs 7,000JPY for a day. If you're on a budget like us (2 pax), do hit me up and we might be able to car pool and split the cost further
By the way, we're in Takayama city between the 8th and 9th of May 2017