Estimating jobs...

Back a few decades ago, I had a country bodyman that did some of my cars. Most tallented person. He did some street rods, and could do anything from body to anything mechanical. . He had several customers that had budgets and $ restraints, so they agreed on a $$ of work to be done every month/week whatever. They agreed on what work was to done that month, and the price. He got is $ every billing cycle.