While, I can see the premise that @Angel-Ty L. puts forth, is an excellent choice if you are strictly targeting 40+ year olds on Facebook; by strictly limiting advertising on both Facebook and Google AdSense you are placing limitations on your reach and target demographics. Spending $1000 on Facebook alone I would call a waste, especially since the fastest growing demographic on Facebook right now is people over the age of 65. How many more homes are the baby boomers going to buy, unless they REIs as well? What I think Angel is suggesting, is that you need to target people with the money to buy with your advertising.
But by ignoring the other platforms, is to give up on a prime demographic of 20-30 year olds that are most likely seeking a new home. This demographic is largely no longer exclusively on Facebook, and are using google less and less to find what they want. Studies have shown that the younger demographic the more likely they are on another social media platform other than Facebook.
The Real Interesting Part of the Future:
The average Tech lifespan is 3-5 years before you either need to revamp or go down in flames. Facebook just did their most recent revamp. People who look to capture their targets using mobile app content will fair far better than those who don't adapt. Even better yet, if you can capture the market using an audio application that can be accessed through Amazon's Alexa or Google Home, will out perform the competition; period. Think about it.
John and Jane are arguing...."Blah, Blah, Blah....I want a divorce....Alexa, find a realtor." Or "Google, where can I locate a home to rent?"
Sure, this may seem far fetched now, but in 5 years, you will have to overcome huge obstacles to reach your target with Google AdSense and Facebook ads. It would not surprise me if Facebook went the route of searching or engaging by voice in the near future....