Ma, most of the systems in our area (NC) cost between $1,200-$1,500. There is some variations depending on the home; crawlspace vs slab, size of the footprint, ease to mitigate outside of the home, etc. You can call a local company and most are willing to give free estimates.
I am sure this may be different for different areas. In our area, you can expect to pay $650-1200 depending on all that is needed and wanted in the mitigation system install. Anything more thant that I would say you would be getting ripped off. Definiely call 3 contractors to get quotes. I had a client whose buyer had one installed in their home for $2500. They were not very happy with their contractor when they found out we had two quotes for under $800. Good luck.