You can buy almost anything online and if you have the skills, tools and patience you can probably install it yourself. All 3 of the companies you mention make good equipment and they will install and service it too but as you have already noticed, you pay a premium for their products and their services. So in the end it all comes down to how much you want to spend and how much commitment you have to the project. Do yourself a favor though and avoid big box store brands like GE and Kenmore units. If you are going to spend the money, buy equipment that will last more than a few years. Fleck is a good place to start since you can't get Clack online anymore.