Then maybe you should start doing some shader jobs?
Those are fun, especially if you do fixed price for single shaders. This way the tasks are very restricted and the fixed price solves the issue with you not working most of the time. To calculate the price just estimate the time you think it will take, double it and multiply with whatever you think you want to be payed per hour (I think I started with 20€/h). So lets say a basic bloom effect without anything else (filtering/downsampling/blur/upsampling/blur/combining) takes you like 3h -> 3h*2*20€ = 120€. The *2 is in there because your estimate will turn out to be wrong and from my own experience it is usually twice my initial estimate . Just be carefull to only do the things you specified in the beginning and not more because that usually turns out to get more and more work you do for free. Sure if it is just tweaking some values it might be fine and if something turns out to break, fix that and you may want to help integrate the effect, but that should be it.
I used to get payed after I was done with the job, which of course needs you to trust the one paying you to actually pay on delivery and not just use your shader, but it would have made it easier for me to get out of the job for whatever reason. While in rare cases people my let you down, I had mostly good experiences and even people paying me a lot more than agreed uppon before.