Thanks for your answers. So the least expensive options are those from the October set at 300 each, or the Fiend Pit for coins and then upgrading it from 2 to 5 for 300. Hmmm.
My policy has for a while been 5 dragon habitats only, but for max 250. I still remember the happy days when for a short while we could get the Fairy Crossroad for 75 gold. Half my island is covered by these.