Although the control of disease by destruction is fairly drastic, (the
UK also controls Foot and Mouth disease in cattle by destruction), the
economics can only be judged on a long term cost per colony basis.
I do not know of any of my bee keeping aqaintances using chemicals to
address AFB. Does the cost of AFB chemicals in the USA amount to more
per colony than the cost of destruction would be per colony (over a long
period of time). Costs would of course have to be averaged over the
total number of  USA colonies.
Of course if the USA was to adopt destruction as policy there would be a
high short term cost.
Disease control by colony destruction has certain advantages since it
will destroy "disease susceptable genes" as well as the disease itself.

Alan Riach
Edinburgh, Scotland