It will pay to have a reputable company to install your system. The cheapest price usually isn't the best way to go. Warranty service, proper installation and maintenance are very important. In new York state there are rebates if systems are installed by a qualified contractor. Some other states have similar programs. This is not a job that should be tackled by an amatuer. If your furnace is less than 90% efficient you may want to upgrade that as well.