PS: @OP - i ended up voting 9900K since that's the performance level you want to be heading towards if availability and pricing gets sorted out. However, if things don't significantly improve by BF/Christmas I would either build using some cheap Intel CPUs and upgrade in 2019, or simply go 2700X and see what those 7nm chips have in store.
Sorry, must have misread it then, though I still can't recommend building with cheap Intel CPUs unless you're implying that he should build on Z390. Many Z370 boards have inadequate VRM configurations for 9900k.
And the cheaper Intel chips have price problems right now as well (8700k prices are up in some places, etc).