Unity is pretty much free if you make < $100k. I have a tutorial series for writing a 2D game in Unity up on Youtube if you are interested: https://www.youtube.com/watch?v=3Vpf6vFOXTQ&list=PLvUqRm2B9R...

Otherwise I'd suggest you brush off you C skills and use SDL.

Or just tinker with Pico-8 if you want some oldskool nostalgia https://www.youtube.com/watch?v=ZuaLuMhwcc8&list=PLvUqRm2B9R...