I don't consider myself a professional programmer. Neither for shaders nor for all the other game programming and design tasks. I also think/know that I cannot professionally work on jobs like this.

These are the main reasons why I don't take jobs like this. I just can't ensure to provide high quality services (in a given timeframe) and there are too many things I'm not able to do, mostly due to a lack of knowledge and expirience.

Also a $-per-hour payment wouldn't work for me because I RARELY 'work' on a project / peice of code / whatever without doing anything else. So just a fraction of the spent time is being invested in actual programming.