@Lori Spadaro - I would recommend avoiding Boulder for Airbnb right now unless you can get a property with an accessory dwelling unit and you can put the main home as your permanent address.

I've done some research on Accessory Dwelling Units as well. 

Great way to recognize an opportunity to add value, I love accessory dwellings!

Our City allows you to build what they call Accessory Dwelling Units in backyards!

It looks like lathe and plaster which means the walls are most likely a thick mud wall with plaster embedded with wire which is a bear to remove, hopefully that quote is for a full gut and replace, but I would just update the floor, have the wall tile painted, tub glazed, new shower fixture, vanity and accessories like towel bar, shower curtain. 

I have been looking at the Nashville market to buy 5+ acres, owner occupy the main dwelling and build tiny homes or other accessory dwellings on the property for short term rentals.From what I gather, AR2a zoning (which nearly all these sorts of properties are) disallow accessory dwellings, but somehow allow mobile homes, accessory apartments, and two-family dwellings.

If the garage could be salvaged, I would love to make a studio accessory dwelling out of it.

I called on retail bicycle stores to sell them bicycle parts and accessories.

Also, I know HomeReady allows you to use gross rent from the ADU (Accessory Dwelling Unit) to help qualify for the mortgage as well, I'm not 100% sure about the HomePossible loan.  

But I try to avoid it mostly if I can, I hate walking into any home and seeing those same vanities and accessories you see in every other flip that were bought at Home Depot.