Replacing some or all of your windows can easily cost thousands of dollars. This is a good place to start. The Consumers Guide to Buying Energy Efficient Windows and Doors is an excellent source of information. This will help you understand the basics of windows and doors, styles and features, to more detailed information on vinyl extrusions, Low E coatings, gas fills, spacers, as well as installation methods. Once you have familiarized yourself with this information you will be better able to access the quotes you receive.