On what hardware? Like companies would buy up GPUs?

Presumably you'd buy really beefy laptops. The price delta between buying the most basic MacBook Pro possible (14", M5, 16 GB unified memory, 1 TB SSD) and one with the M5 Max with 40 GPU cores, 128 GB unified memory, 2 TB SSD is $3400. How much Claude usage does that get you/in what time does it pay itself back?

That doesn't get you any Claude usage. Claude models obviously aren't open, but equivalent models to Opus take about 400GB of memory to run.

You can run the versions with fewer parameters or quantized weights but depending on how much quality you're sacrificing, now you'd have to compare the price against cheaper Claude models like Sonnet.