Rock Bottom Prices Not Always Best!
The range of prices should not be excessive; you shoudl expect 10 - 15% between the top and the bottom; be suspicious of a very low price.
Write back to contractors thanking them for providing a quotation. It can be helpful to them to know what the lowest price was,
but do not get drawn into any offers of reduction or price-matching, as the contractor may be tempted to look for ways to recoup the shortfall.