Prisoners to our Environments

Have you ever noticed that prices from contractors or tradesmen seem to be higher after they see the homes we live in. That after they see the size of the house they try to push more expensive repairs or upgrades onto the home owner. In my experience it seems that the nicer and the bigger the home the more the price of a job goes up. If we live a modest home it doesn't seem to change all that much.
Case in point,yesterday I was out on a call. A very nice home, retired couple, trying to deal with an allergic reaction problem in their home ( IAQ ).The contractor of the sub division they live in has gone to all lengths to help resolve their problem. The couple had nothing bad to say about him.
Their home is a ranch style on a crawl space. The heating system was 95% properly sealed. Their complaint is allergens in their system. First thing I noticed entering their crawl space was the amount of dust in it. It had never been cleaned. They had brought in heating specialists who are trying to convince that what they need is a HEPA-FILTER (top notch filtration system) and a HRV (heat recovery ventilation system). I have no problem with either of these two solutions however in my opinion that's not where they should start. They are talking thousands of dollars to install these two items into their system when i fully believe that they should 1st look at spending a couple hundred dollars on my ideas to see if they rectify the problem. Retired couple,nice home, they gotta have lots of money.RIGHT???
They already run a very effecient filter in their furnace. The problem is the amounts of dust in their crawl space. Spend a couple hundred dollars to get it cleaned out, finish sealing the 5% of the system that wasn't sealed 1st hand and BOBS YOUR UNCLE!
If I'm wrong and I don't think I am then they can go ahead and spend the thousands to up grade the system.