This is NOT a code conversion service

Do you really need to convert code as you can use C++/CLI to make an assembly that allows to use C++ code from C#.

Converting lot of code can be time consumming and error prone so you have to be sure it is the right approach.

Offen find and replace can works quite well. It all depends on the size and complexity of the code. by the way, I usuall prefer that over convertion using IL has in that case comments are lost and some primitives like for loop are replaced by while loop and other similar things.

A paid tools that works well might be more cost effective than a tools that don't work that well. You have to try yourself with your own code as support can vary widely...