You might be coding in C already.
Objective C is a strict superset of C. Just use Objective C, without using classes, objects and methods, and you will be using C. Then put the code in .c files instead of .m files, and you're done.
You can do almost the same things in C as in (manually memory managed) Objective C by using structs and passing them around as explicit function parameters (instead of as the hidden parameters in Obj C methods).
But have you checked into coding Python modules in Objective C?