Do we have to pay to install custom rom? So I want to root my Android and I was wondering: Do we have to pay for installing a custom rom or is it free?
In general, Custom ROMs are FREE. To date, I am not aware of any custom ROM that is paid (at least for the custom ROMs I have used for my Samsung Galaxy S2, S4 and Nexus 7). However, you can donate to the developers if you wish.

Rooting and installing the custom ROM yourself is free, assuming you accept all the risks, which includes bricking (or destroying) your phone. 

If you are not confident enough to perform the rooting and installation of a custom ROM, you can ask an experienced person to do it for you. Of course, they may or may not request for payment.