It sounds like your cleaner is charging more no matter how many people stay, so I would recommend upping your nightly rate a few dollars to make up the $50. 

The longer you wait, the more chances there are for problems, which means dollars out of pocket, which means added cost to the REI, and even more of a delay to the profit point. 

However, if I'm just looking at the structure/improvement I believe that a home would depreciate following a curve in the same way that most physical goods depreciate on a curve (in terms of real dollars, adjusted for inflation). 

Every dollar made was put aside and then used to reinvest in another property.

So I made a compromise with myself, instead of putting that $100 directly to my principle, I'm opening a brokerage account that will have $100 deposited into it automatically every month and invested in index funds using dollar cost averaging method.

The lower dollar loans have a very high percentage in closing costs because the cost to underwrite a $500k loan is the same as a $75k loan unfortunately.

As near as historians can figure, Washington’s net worth at the time of his death in current dollars was over $1 billion.  

Thats the million dollar question. 

This works best on used homes where the price is only a few thousand dollars, but if it is a brand new home worth tens of thousands you could offer to help them sell it.

There are multiple billion dollar companies dumping money into the city, such as Intel, Google, Honda, and Amazon.