The main cost with every new host is that it needs a monitored, smart uninterruptible power supply (UPS), preferably a dedicated one due to its limitations of a one-to-one physical connection to a single host Securing multiple hosts wherein one provides the UPS monitoring data to the others might introduce points of failure preventing the graceful shutdown of those other hosts, though I have set that up untested with my fingers crossed.
This is why one computer that does the work of four, such as one with 256 GB RAM, a 48 virtual core processor, and many more PCIe lanes for multi-port network interface and storage controllers that can be passed through to virtual machines. It might be prudent to consolidate even at a cost equal to the sum of individual computers for such a system, since it eliminates the hassle of sharing a UPS and likely consumes less electricity with lower heat dissipation than four physical PCs, and allowing greater runtime when on battery power.
A reputed, well-supported, smart and especially a rack mountable UPS is obtained through a B2B reseller, which translates to higher costs and hassles of both initial acquisition and periodic battery replacement.
Consider these additional “costs” as well:
You need a cool secure space away from possible water damage, with hardware either locked up or at least not having accessible removable external storage that is easy to steal.
To access the PC at the console for maintenance, you might also need an IP KVM switch, usually one for each PC, especially if distributed due to space constraints or to mitigate the risk of physical loss. I use slower, somewhat glitchy, host bus-powered single-port nano KVMs for occasional management rather than an expensive multi-port one that I only ever had in the wired VGA/USB era. A higher-tier Pi KVM is reserved for accessing the Intel-based Mac mini server remotely since there is no Apple Remote Desktop (ARD) for non-Mac clients and VNC viewer does not scale the display resulting in a scrolling mess.
This of course makes sense only if one does not require physically separate hosts such as for high availability or locational diversity. Not having a remote location except a t2.micro (1 GB RAM) FreeBSD instance on AWS, I have chosen to separate hosts across floors, coupled with automated off-site backup. The basement utility closet with the water supply has a wall-mounted (hence off the floor) mini rack for the essentials at the utility point of entry, whereas the larger and noisy equipment like a NAS with 7200 RPM spinning drives, and a Proxmox host is across the passage on the same floor on a non-conductive wood stand with feet.
File-level backups of configuration files backed up to the NAS from the various services are synced to TrueNAS SCALE (see Home Lab II) as a second copy two floors up, with ZFS snapshots of that copy to TrueNAS CORE in a full-sized rack starting this quarter once I order, receive and set up TrueNAS Mini R in the full-sized rack upstairs. A very costly unit once outfitted with under-provisioned power-safe data centre grade SATA SSDs for performance storage in addition to quiet NAS HDDs.
I would not put noisier surveillance HDDs in a NAS unit that I could already hear from across the hallway, considering the ambient sound level is 32 dB without, and the Mini R is stated to be 45 dB. Noise is a price I don’t ever pay, so I might have to move systems around if the security NVR project ever gets off the ground.
Off-site backups are automatically uploaded on a schedule to one or more cloud storage providers. Often, there’s an additional cost for proprietary cloud backup with dissimilar products given that even S3-compatible storage integration does not work as universally as intended.