If 10% ownership costs $79,900, is this a $799,000 cottage if it is sold as whole ownership?

No, not based upon direct market comparables.  Fractional Real Estate pricing is similar to other items that you may buy only part of.  When you buy one slice of pizza, you pay a premium for buying just one slice.  But when you can’t eat a whole pizza, (ie – you don’t have that much vacation time) why would you buy the whole thing?  When you buy Fractional Real Estate (like buying a slice of pizza), you are buying what you will actually use.