[jpalomaki]

Is there some maintained "bang for buck" chart available that would show how many units of certain performance metric one $ buys with different CPUs?

[throwawaymath]

Yes, you're looking for the Passmark "Best Value" ranking: https://www.cpubenchmark.net/cpu_value_available.html It's also helpfully represented as a scatter plot: https://www.cpubenchmark.net/cpu_value_available.html#multic....

Unsurprisingly, older generation models tend to dominate that list. Keep in mind that the thermal efficiency for Xeon v2 and v3 models is lower than v4; Passmark does not include power draw in this ranking. If you can afford the extra power usage and don't mind DDR3 RAM, high clockspeed + high core CPUs can be had relatively cheaply by going with V2.