My estimates are normally the complete project price, and I allow for unforseen surprises, but I have a unique situation (at least it is unique for me). There are too many unknowns in a retaining wall removal and replacement, such as what was buried, boulders, as well as addition of boulders at the end. For example, while I'm looking at a minimum of 5 tons of boulders ans a minimum, I really think it will take more, but their budget has a ceiling, for now. My point is that while the homeowner and I both know this project is open-ended. I want to ensure I cover myself adequately in the quote. Any suggestions?