Shipping container costs went up after covid, but still, at their peak you could buy one for ~$5k, $500/month is insane rental price especially if he never moves it.
I looked up prices for 40ft container: pre-covid: Under $2,000, Peak Pandemic (2020-2021): >$8,000; 2022-2024: prices falling, Current: $2,300
I looked up prices for 40ft container: pre-covid: Under $2,000, Peak Pandemic (2020-2021): >$8,000; 2022-2024: prices falling, Current: $2,300