How did you find this deal and how did you negotiate it?

Cost to build should not matter there.Look at your deals. 

You need to start by asking the seller what their true financial needs are out of the deal.

I've tried to make my own spreadsheet which makes more sense to me based on my current understanding of deals.

. - Management: it may be hard to manage the home if you are not living in the area, to deal with emergency maintenance or make sure the home is getting taken care of.

Considering general scenario 10% for property manager and 3% for realtor and manager say 5% or fixed fee the 1st investor cost is coming to 18% so adding 5-10% on basis of future deals and partnership I can think of 25% - 30 % would still be great deal for 2nd investor." 

We have two other investment properties that were purchased on market, this is our first off market deal.

Hey @Atlas Blake, so the catamaran idea seems kinda separate deal to owning a STR.Is the plan to maybe buy or build up a small resort type place and do the catamaran thing as part of the stay?

It is an off market deal, and is fully renovated in 2020.

I've tried to make my own spreadsheet which makes more sense to me based on my current understanding of deals.