I was just in Japan and HSR between Tokyo and Kyoto run every 15 mins throughout the day. It’s a distance of 450 km and takes just over 2 hours with 2 stops. Cost is 140.00 AUD each way plus a reservation fee
So considering this, I reckon a trip from Sydney to Brisbane in the mid 2040s if operational could likely cost 250.00 AUD each way. The time to take the trip would be a minimum of 4.5 hours, at a speed of 250 - 300 kph