A wireframe-only design service where clients fill out a detailed onboarding form and then receive a wireframe of their app idea for a fixed cost.
Clients can practice communicating their ideas clearly enough to get effective results in a low-cost, low-tech, fast-feedback environment, and then they can use the wireframes they produce to save time and money when they start communicating with more expensive programmers and designers.
Revisions will cost the same as the initial design; it is up to the client to communicate effectively and refine their vision. It's like a read-eval-print loop for cheaply producing wireframes.
The design service could also include a library of design options, to help clients get ideas about what is possible and discover the terminology they need to communicate better with designers and programmers.
If you want to read more, subscribe to my personal newsletter.