What kind of cost though? Actual silicon/chip cost doesn't matter because it's amortized over so much usage. Energy efficiency matters, but more as it affects achievable density. For most server applications latency is king, which is why servers use big x64 chips with all power saving features disabled. If you have an application that isn't latency sensitive, it might make more sense to just use a big Xeon or EPYC CPU that is running in low voltage mode.