Bud, if you look at the time requirements, I think you'll find it takes around 3 hours to do one of these, if not more. First, you get the phone call to ask about the service, which often requires ~15 minutes to explain what a blower door test is in the first place, because the caller has no clue. A few people have called me early in their building process and basically want coaching on how to build so they will pass... telephone consulting. Then, load up the truck, drive over there, do the test. Load back up, drive back, put the gear back in the shop. Then, sit down and write the invoice, email it off.
None of my jobs are more than 12 miles from home. I almost always lose 3 hours of actual working time to do one of these, and have been charging $180. Mine include an emailed Tec-Tite report and some info on what air leakage and ventilation is all about. Sometimes I get followup calls from the builder or homeowner wanting to know more. At $180, I am just barely replacing the lost construction income, since I can go out and work my contracting biz for known money during those same hours.
Not sure if the foot-in-the-door guys will want to do freebies. These are new homes, there's nothing to sell except maybe furniture.