Dave Burke often hears from customers seeking a competitive bid. That’s possible with a full set of plans, but only if the owner has acquired a complete and detailed set of plans. When the plans are incomplete, it’s really difficult, even impossible to give an accurate bid.
You’re better off interviewing 3 different general contractors in person and then award the job to the one with whom you feel most comfortable and who understands your creative goals, schedule, and budget range. Then you should get competitive bids from sub-contractors and trades professionals.