I am not dyslexic but a good PhD friend was. What she did was break up the work into shorter bits and asked everyone that she could to proof read parts of it. That included; supervisors, other PhD students, friends, technicians, family. Quite regularly I would get a a page or two to proof read even if I knew nothing about the topic. So if you want to do it for free, if you break it into manageable chunks most people will help you.