Looking for some suggestions on dedicated severs, I understand them but have no clue on what spec's suit my needs. Have been suggested Nocix and their prices seem decent.

If we are using Noxic severs as an example (https://www.nocix.net/dedicated/), What would be the cheapest one able to run 15-20 bots?

Cheers.

many things need to be taken into account, like for example, the RAM usage from each client can be different, so first things first, find out how much memory each client uses x20 and there is your minimum ram, then cpu can work out by googling and seeing if it's a piece of shit etc

Passmark has useful benchmark scores that you can judge these processors by. Though, remember that it's just a single benchmark number and doesn't tell the full story.

You can compare it to a computer whose performance you know, and use math to estimate the expected performance of the servers.