xAI built the Colossus data center in 122 days (just the physical construction time).

Colossus initially had ~200k GPUs. 100B buys you ~1 million high end GPUs running 24/7 for a year at AWS retail prices.

Initial Colossus buildout was 100K GPUs

They also reused an existing building that happened to be in the right place at the right time. The larger data center buildouts would almost always need new, dedicated construction.