Modular Garage as ADU?

[Justin Knighten]

I'm considering having a 2 story detached garage built on my property with an apartment above it that we could rent out long term or, ideally, AirBnB out.  I've found a company called Sheds Unlimited that sells what I think I'm looking for and it'd be about $40,000 delivered and installed.  It'd be bare wood on the inside and I'd have to have it finished out.  I know it varies from place to place, but what is a rough number on what the concrete foundation (24x30) and finishing out ~700 feet of apartment would cost?  I can do a some of the work myself but would sub some out.  

Anyone have any experience with this company or concept?