Please bear in mind that permit drawings are not complete plans and contain limited information about the final design of your space. They provide information about the general layout and structure but have limited or no information pertaining to finishes, interior architecture, custom millwork, lighting and electrical features. This is the information that your contractor will need to give you accurate pricing before you start construction.
If you have the detailed set of plans and the specs that I mentioned previously, you will get “apples to apples” pricing from the contractors bidding on the job. And the contractors will have to stick to their provided pricing because they had all the information in their hands.