Building/running your "own" cloud doesn't require owning bare metal servers. You can rent and lease for a fraction of the price of renting cloud instances. Once you start paying up front of reserved instances, the capital invested tends to start stacking against you.
You certainly can burn through ridiculous amount of money if you insist on purchasing servers outright and pick expensiv brands.
Conversely, the "private cloud" deployment I run are mostly rented servers with month-to-month contracts. No upfront infrastructure spend - we grow them a server at a time. We also run some bare metal setups and they're generally cost-competitive with rented servers, but there it certainly depends on the size of the installation.