High Bid, Low Bid, Best Bid?

I’m on the board of a seven-story cooperative in Forest Hills. We are planning to replace our roof, rebuild sections of parapet walls, and make miscellaneous masonry repairs throughout the exterior. We had three contractors check the conditions and give us quotes: the low bid came in at $215,000, while the other two were at $310,000 and $425,000. The wide gap between the low and the high quotes has us concerned about the accuracy of the figures. The high bidder comes highly recommended by a shareholder, but his price is beyond our budget. What’s the best way to ensure that we’re receiving competitive, yet realistic, bids?

What goes into a bid
The bid sheet should contain an itemized break down of individual components so the bids can be compared more accurately.
The Bidders List: Some, Not All
Don’t Spill The Budget Beans
Bargaining For Reductions
Final Bidder Evaluation