First no equipment, parts, or install prices. Its in the rules. You should edit it out.
Around here, we're below freezing temps quiet often, We pump the condensing furnace into the sewage drain to prevent from freezing. Your local codes may not permit that.
Although it may not at first the efficiency increase is worth the cost. With the increase in fuel prices, it does pay back.
I have done the heat in many houses with basements with 3 exposed sides. It still does not jump the heat loss that much.
What is your winter design temp. Or what area do you live in.
If you want, you can do your own load calc, http://hvaccomputer.com/talkref.asp
To find out for sure.
If your outdoor design is -30, it might need bigger furnaces.
If thats the case, make a deal to pay the contractor to install the larger ones then.