Ryzen 9 5900X won't be cheap anytime soon, especially not at the moment of Zen 4 launch.
It will be years and if only there are considerable performance improvements coming.
I never said cheap, I said cheaper.
Look at the 3900X. On its release it was selling for around £480, Now can be had for £360 on a deal.
Maybe we won't see as big a drop but it will.