The Project Bid Process
You will want to get several bids from local contractors to find a quality window at a fair price and to find the right installer at the right price. As a rule of thumb, installation is half the battle when replacing your home windows so understanding the installation basics is a good idea. There are several types of installation that have varying degrees of difficulty and price tags associated with them.
At the end of the bid process, there should be a general consensus on the type of installation you need. If the contractors are all saying something different in terms of the extent of the work required for the install, get more bids until the answer is clear to you. Remember the bids are free so there is nothing to lose (except your time of course, but hopefully this will be more than worth it in the long run).