How costly it is to generate a random number in terms of CPU usage?

Answer 1

Depends on the implementation used. See here for pros/neutrals/cons to get an idea (in other words...which algorithm?)

http://www.pcg-random.org/other-rngs.html

c# reference (Random class? or System.Security.Cryptography...? Perfmon might help here)

http://stackoverflow.com/a/23481245/3981745

Answer 2

C# Random.
It's very useful for Unity.