It is hard to do. You can explain that what should have taken x hours, took x+y hours because of his many changes. You cannot work for such low-income. So your

It is hard to do. You can explain that what should have taken x hours, took x+y hours because of his many changes. You cannot work for such low-income. So your new rate is what is reasonable in light of the past experiences with him. If he doesn't agree then so be it. You do not need an unreasonable client who won't pay a fair price. To make a profit in any business, you need to charge a fair price. That is, deliver good work and know the value of what you provide. Subsidising other people's businesses is not healthy.