Greetings.
I know how to build an in house game engine using OpenGL that can have its own physics engine, Physically based rendering with deferred shading, skeletal animation, particle systems, destruction, tesellation or most other things required in a custom game engine.
If you want, I could work on some of your tasks or a prototype as a test (without any cost of course) for you to assess my skills. I usually finish them quickly.
Also, because of low per capita of my country, I am willing to work for prices as low as 7-10$ hr.