Getting Contractor Bids and Evaluating an Estimate is something you need to know how to do to protect yourself and end up with a successful project. It's also not fair to a good contractor who does a detailed proposal and includes a full scope of work, to have their price compared to a fly-by-night company who throws a low-ball number out there just to get your business.
Most contractors are hard working and knowledgeable pros who want to do a good job and an informed consumer is often their best customer. So read Getting Contractor Bids and Evaluating an Estimate and learn how to scope a project, understand what to look for in the bids of different contractors like painters, roofers, plumbers, etc. You'll learn that what is "Excluded" in a bid is often as important as what is "Included" in the proposal. And don't forget to read about how to evaluate price, payment terms and what it means if your contractor is proposing "incentives" to you.
With a little preparation you'll be able to communicate much more successfully with your contractor, and you'll both enjoy the process.