Thus we turn to legal contracts which specify what is to be done for what amount along with every other detail concerning the transaction. I would recommend this process for good friends, when it comes to any significant amount of money...
Just out of curiosity, why don't you do it yourself? You may find it much more rewarding. All the tools are free.
Professional Windows compiler: here or here.
Professional C/C++ tools: here, here, and here.
Professional 3D animation studio with real time physics engine: here.
Professional image manipulation and touch up program: here.
... that's more than enough to get you started.