Tumba - $1 - $2k (try real estate agents if they make just one sale they'll be ahead) you could also put up a directory and charge businesses $10 - $99 (lot of work though)
Tura Beach - put up some pictures and text and sign up to Booking.com then when it's ranked in the top 10 approach the 50 odd accommodation businesses direct by saying they'll save 15% on bookings through their own website vs AirBnb or Stayz. (say $150 per night x 100 nights per year x 15% forever) that will give you an idea of value. Again local real estate property managers should be interested.
Tallangatta - CPC is $0.00 so about the same for value.
Yarrangobilly Caves - the number of businesses who could monetise it are close to nil, so $0.
These are the metrics I look at; search numbers, CPC, and number of accommodation places (search Stayz and AirBnB about 2 for Tumba and Tallangatta and 50 odd for Tura Beach).