Long-term rental rate rule of thumb for owner-occupied

[Matt Zale]

For some that are starting out in REI, the owner may have to occupy the rental property. Is there a rule of thumb on determining a rental rate for owner-occupied properties? Let's say the owner stays in the master bedroom of an 'average' 2bed/2bath detached house, with just one entrance, while renting out the other bedroom to a 'housemate'. If it helps with any rate adjustments, the owner would not be using much of the common space and would travel more than usual.

Would it be as simple as finding the average or median neighborhood rate and splitting it 50/50? 

I'd probably be better off doing Airbnb, but need accurate data to justify the Airbnb option. I was also a little concerned about some conflicting info between sites like RentCafe and RentJungle.