Today you can already get 51.2 V, 16 kWh batteries complete with balancer and BMS from a European supplier for 1200 € (1400 US$): https://www.nkon.nl/novat/nkon-ess-eco-s-51-2v-16-1kwh-thuis...
[1] Three-phase wiring in homes seems to be very rare in the US, but is extremely common in Europe.
But you're right, most installers do high voltage batteries.
I'm just pointing out this is way lower than typical pricing