I guess the question is how much do you like the house? 16ppm is very high iron (mine is 12ppm last check). The good news is its treatable, the bad news is its gonna cost you. Knock 15K off the asking price just because of this! You can fix your iron problem for about half this assuming you can live with average (not spectacular) water pressure. Also you may find that the high iron has damaged your pipes, water heater, dishwasher etc so be prepared for this possibility
What type of well do you have? How deep is it? What is its GPM recovery rate of the well? How many GPM does the well produce (get a 5gal bucket, open up the outside faucet, see how long it takes to fill it, and do the math) What are the low/cut it, high cut out water pressure readings on the gauge at the pressure tank? Do the neighbors also have high iron and sulfide smell? Is there anything else you can tell us about the well itself???
What type of filter system is installed currently? What is its approximate age? What were the recommendations of each of the four water treatment companies? DO you want someone to install this for you or are you up for a moderate DIY project?