To me the best deals on habitats are: Buccaneer Bay - 200 gold to hold 5 dragons; Shimmering Shoal - also 200 gold to hold 5 dragons; and Crystal Hatchery - 240 gold for 5 dragons, but it is also a Fountain of youth habitat and it hold a variety of colors: gemstone, white, blue, and red.

Many habitats on sale for 200 gold hold 4 dragons but are upgradeable for 100 gold, but that means you are still spending 300 gold to hold 5 dragons. Not a bargain.
I used to buy all the habitats I wanted based on their appearance, but now that I have most of the habitats, I am a bargain shopper.

As for dragons, i would say Daywing (Ultra Rare Champion) for 240 gold is a hot deal. I'm trying to collect all the Rainbow Dragons, so an UR Tropic Tide for 270 gold isn't too bad. Nautilus is also UR and 240 gold, and it's a pretty neat dragon as it transforms at each stage.

I'm sure there are some other good bargains in this sale, but those are the ones that caught my eye in particular. I am interested in a few others, fortunately they all have blue element, so I could buy a Shimmering Shoal and house all the dragons I am thinking of buying except for Daywing.

Just my 2 cents. Feel free to chime in with any other great bargains you have noticed.