jonkeane do you have the game done? then send us characters images , or better use camasthia studio to capture game play and send us. and in your price we can provide 2d aniamtion and maximum 30 seconds . make your budget 300usd to 400 usd
It does seem impossible to do. You need to provide the original 3D files, otherwise to draw objects and animate them for $100 would be impossible as it will take a lot of time and resources and many people have to work on it.
I wished to participate, but without the original 3D file, I am sorry, but no way.