It really is so much cheaper. After dropping S3/RDS/ECS for OVH bare metal running Proxmox, my costs decreased significantly. I still use Route 53 and back up to S3, though.
My "one weird trick" for spotting this behavior is using my middle initial on LinkedIn. LinkedIn stores it as a part of my first name, so their spam always starts off with "Hey Mark P.!"
Those emails get ignored. I ignore most automated agency emails as well.
I will always reply to personal emails from in-house recruiters or employees, however. I am starting a new job soon, though, so it's only to thank them for writing.
Before purchasing and installing your own server, I would try out a bare metal server from a company like OVH for a couple months. You'll get a better sense of the additional setup steps necessary (as compared with a VPS) without buying hardware or committing to a collocation contract.
I've learned a ton (and saved a bunch of money) transitioning from EC2, RDS, and Elastic Cloud to a single OVH dedicated server running Proxmox to host multiple VMs.