The issue is that if you are dealing with an inexperienced client, the project you are quoting for and the project another consultant is quoting for is not the same project, especially if it's an "MVP".
I like your comparison to website building during its early days. Gives us the benefit of hindsight. One consultant was going to take a html page from a previous project. Find and replace the client's colours in. Make 5 pages (home, about us, product catalogue..) and then wait 6 months for his client to fax over the "content."
Another consultant was going to use coldfusion to make a dynamically updating copyright notice, & contact form and use templates to make the site "ecommerce ready". He was going to hire a copywriter to work with the client. And (as an optional extra), do CSS.