I don't see the prices going lower, the only way you would pick one up in the $70k's is a high km example, I know of a few that were bought in this range but for 2016 they had 80,000-90-000 kms. Not a bad option as 100,000 kms is just breaking in the engine on a Lexus 2UR 😃
Production concluded is total amount of GSF's sold in Oz is 141, so its likely prices will decline slowly until they fall into hands of enthusiast and they will start to climb.
Look at the ISF for an example.