Its a very gross rule of thumb that has a fistful of assumptions.The 50% rule, OTOH, has been borne out by several large surveys.

There is not a single beneficial feature of the sewer lift station compared to standard gravity drainage.However, once our crew dug up the street and compared the height of the City sewer main to our surveyed top of footing mark, it became clear that, with standard slope, we could slide the sewer pipe just under our footing.

[X] ENVIRONMENTAL SURVEY: Within ____ Days After Acceptance, Buyer shall be provided a phase one environmental survey report paid for and obtained by [  ] Buyer, [X] Seller.

One word of caution - I am going to assume that you never had an asbestos survey done.  

Paid online surveys (not a good use of time)Use Honey or Ebates or other discount portals for Amazon/eBay or other internet purchases to save a few %Certain credit cards provide 5x bonuses (Chase Freedom has rotating categories) and Chase Business cards are good for auto-pay things like internet with extra bonus categoriesMake a Ghetto Latte at Starbucks and other funCharging up your electronics/phones/Gameboys at work before you leave for the weekendI never paid for Tinder plus or extra coffee beans on When Coffee Meets Bagel 

They make a product and then find people to purchase or then survey the people and create a product to fit their needs.

Does that include the studies, surveying, etc?

Appraisal, survey, title, ect...http://www.houstonhotdeals.com/Rltr1.htm

This same department has cited us for $250 lawn care for an abandoned property next door to another rental we own & again we go in to explain it with a survey & again we have to go to housing court clerk to straighten it out.In another town we have been inspected & cited mid-winter for gutters damaged by ice yet the home across the road has had a torn tarp with multiple (torn shredded) layers on its roof for 5 years.

Business Model……………………………………………… 138The Inspection Survey………………………………………………… 139H.I.