Not a dumb question. Start with the truth. “I’m trying to gather more info to determine if I can move forward with this project.” Then after describing what you’re thinking, ask them if they’d be willing to share what level of finish and what the $/sf was on there last few projects.

Like others have said, $300 is a good target. Contractors are going to give you a better idea of budget. Architects and designers are good at what they do, which is design. Don’t let an architect be your estimator