Recomended game engine for a Life RP Game

Hi, I am searching for a Game Engine to create a Life RP Game such as GTA V or Gmod RP, but with larger maps, better graphics, custom features, etc. Which one would you recomend me?

The game will only be played by my friends, and it will be free for all of them, it won't be sold on any site, at least for now, so the using of copyrighted models, code, etc, doesn't really matter. We also have a budget of nearly 250-500$ to invest on Marketplace things.