mainframe pricing usually is not by pound of iron but per cpu cycle. unless you say nah I'm buying the thing, not just cycles. soyou have a choice of cloud pricing or hardware pricing.
for significant pure Linux workloads that need an own on premise cloud the TCO pricing is surprisingly competitive with any home grown solution.
even if you don't _need_ an own on premise cloud, AWS and similar donate come for free and there may be a break even there, too.
that said, legacy host software, Delphi, cics, Oracle, DB/2, cobol etc, you named it, yes that's a different story, with all the extra software licensing.
but a pure Linux mainframe is surprisingly competitive not just in compute and throughput but also in pricing.
plus you get quite some high availability in silicon. think ECC on the ALU, hot stand by spare CPU, multipath everything, if your business depends on uptime your system architecture becomes much simpler on highly dependable hardware.
so that spreadsheet compares own people and software construction vs IBM tax in some columns.
lol I start sounding like an IBM sales person https://www.ibm.com/products/integrated-facility-for-linux
I just did Linux on Z for a while and I loved it, so please bear my enthusiasm :-D