Currently 4.29 EUR/month VPS on Hetzner. (Although I have some fun features planned and might need some more processing power so I might upgrade in the future.)
They have great AMD-based VMs, 2x perf/$ over Intel. (I've benchmarked.)
I am currently using a bunch of AWS technologies, e.g. AWS EBS, RDS etc. I am also thinking to consolidate all projects to a single AWS LightSail, which offers pretty cheap instances, e.g. 512 Mb, 1vCPU, 20Gb SSD for 3.5$/month.
It was quite some time ago so I don't remember exactly, but I've basically used one of the usual benchmarks that everyone uses to measure the number of requests per second that a server can sustain.
(I've rented another VPS in the same data center and ran the benchmark from there.)