Variables that might change that number would be size of house, number of beds, extra duties you want the team to do (like fetch supplies) and perhaps the drive to a remote area. 

Targeting single family/duplex/triplex/quadplex with 3 beds and 2 baths per unit, and $300K or less.

got it, thanks. and you said u see around 70/month for that 3 bed SFH?

A two bedroom 1,300 sq ft cabin is going to go for way less than a 2 bed, 2,400 sq ft cabin.One of the issues out there too is that some are setup as legal 2 bedroom cabins because of the septic but then they have lofts and such that allow you to rent them out as 3 or even four bedroom cabins to improve the rent.You mentioned one nearby you with a similar layout.

The problem is at $250K what are you getting each side sqft, bed/bath count etc.  

However a couple larger items that should have been discussed: the pipes would freeze every winter (we've since found a fix), no water shutoff exists in each unit, the well pump has to be turned off and cut water to all 18 units, no pest control was ever done on the property, there was a unit that would take on exceptional water during rain due to improper prep and installation of a new concrete slab.

Quote from @Jimmy Sont: I'm looking to build around 700 sq ft 2 bed / 2 bath guest house primarily used for short to mid term rentals.

This property was also an on-market deal.The property was a 4 bed/1 bath single family house.

It is 4 bed/2.5 bath. 

As a two bed with office it may or may not be worth less than a 3 bed but probably.