I read many thread on that topic but were all 1-2 years old. OnGUI is so heavy on performance in Unity 4? I’m doing a JRPG battle GUI but I don’t know if I must end here with OnGUI and begin with another method… should I?
Keep in mind that I don’t want to do a big commercial game (probably I won’t earn anything) so I don’t want to buy a new GUI.
Game’s platform will be PC, not Android or iOS.
Thanks 
It will probably be fine on PC, as they have much better hardware. But there are free alternatives for GUI. Look up Orthello 2D Framework.
I personally don’t think that the UnityGUI is sufficient in any way. For what it delivery it simply requires too much codeing in my eyes. Plus it is not very good in terms of hardware optimization as it will produce quite a lot of draw calls.
So I personally would definitely recommend to have a look at the package out there, and not waste a single minute on trying to implement UnityGUI.
In fact, you could try out some of the frameworks for free to see the performance - eDriven.Gui Free Edition.