Unfortunately this has been the most mild so far.

Sometimes there is only great recession data, and that recession was pretty mild on some asset classes, versus previous recessions.

Duct cleaning costs $280-400 depends on detergents and kind of service, numbers of openings - big house might get more expensive. 

Someplace near water, within an hours drive from larger city,  and with mild winters.

Spray the stone down with a mild cleaner like Simple Green and let it sit for a few minutes.  

Work began last week just with mild demo etc...

FYI @Joshua DorkinI have been using it on some posts the last few days and the issue with it not actually tagging the person seems to have gone away.It is still doing the thing where it goes to the next line after tagging the person but that is just mildly annoying.

Dumping coffee grounds or grease down the drain, using powdered detergents (both laundry and dish) and flushing feminine hygiene products are killer on your septic system.  

You can get the renovations done in mild weather, avoid huge heating/AC bills (or burst pipes if you do not keep the heat on in winter), and get it ready for rent at a time of the year when there is a lot of demand for rentals.

In the past, I've scrubbed it off with mild success, treated it with bleach, pressure washed it.