not sure if this is still relevant but when I work with Architect's for commercial projects (restuarants) we agree on a flat fee up front for the drafting of the drawings, stamping of the drawings and issuance of schedules (required for a building permit)
this is usually in the $3-4k range
However, depending on the scope of your project you can hire an interior designer to do the layout, design, etc. this will work if no architect stamp and schedules are required, this would be significantly cheaper.
DM me with more info and I will point you in the right direction