Hardware is super cheap:
-A 40 slots rack, with gigabit fiber, dual power and a handful of public IP addresses, costs on average 10000€/y.
-A reconditioned server on eBay with 16 cores and 96GB of RAM costs 500€ (never seen them break in 3 years).
-A brand new Dell Poweredge with AMD EPYC 32 core and 64GB of RAM will cost 3000€.
-Storage is super cheap: 500GB of SSD costs 80€ (consumer stuff is super fine as long as you wisely plan between redundancy and careful load) and rotational disks are even cheaper. Never seen a rotational disk break.
Once bought, all of this is yours forever, not for a single month. You can pack very remarkable densities in a rack and have MUCH more infrastructure estate at disposal than you would ever afford on AWS.
The flip side of the coin is that you need operation expertise. If it's always you, then ok (although you won't be doing much more than babysitting the datacenter). Otherwise, if you need to hire a dedicated person, people is the most expensive resource yet and that should definitely be added to the cost of operations.