Aaron, how did things work out for you? 

Also do occasional hot yoga (which will make you feel like a completely new person - and my wife loves it!)

So I thought to offer the option of "I will carry the remaining $10k and work out terms favorable to both of us."

I would be willing to work out a deal if you are interested.

Some replies here, such as the one above, point out that one can work out estimated expenses from the purchase price.

I personally like to stay in mine for 3 days atleast while I setup to know my properties more intimately and to work out the bugs which would be problems for guests.

Sadly, it didn't work out, but there are some other products out there offering a similar idea.One of them is a relatively new product called Tellus (https://www.tellusapp.com/).

As far as what will work out is up to you. 

Sellers motivation shouldn't factor in what you can afford, thats a bonus if they will negotiate, but your numbers have to make sense to you and work out for multiple exit strategies (str, ltr, sell etc)Running the purchase numbers is pretty straightforward, use almost any online mortgage calculator, make sure you know taxes and insurance (taxes will go up a bit if it is currently owner occupied and you don't plan to live in it) Once you know your mortgage amount then start looking at other STR's in the same area and same size/amenities and see what they are getting per night and how many nights a month they are rented to calculate what you MAY be able to get.

Release guarantee if the tenant you place doesn't work out, let's say in the first 90 days and maybe 1/2 price for the first 180 days.