You Get What You Pay For
Your goal should not be to always look for the lowest bid, but rather for the contractor and bid that gives you the most confidence and meets your expectations the best. There may be large disparities in prices you receive from different companies, as with anything else, “you get what you pay for” and the best contractors for your job will not always be the cheapest, but the price should be reasonable for the work to be done.
Make sure that they are on a “level playing field” by contacting companies of the same caliber, qualifications, size and standards.
Always ask for references, proof of liability and workers compensation insurance and the contractor's license number.