Another good area to expand to (even better than the lower green plots) is the "first purple section" that has 6 plots. All 5 plots that are on the same plateau as where the Hareon is, are cheap to clear of obstacles and take only 20 minutes of obstacle clearance times.
The Hareon plot takes 5,000,000 to expand to, but it does give one of the breeding ingredients for a Money Badger.
The Treent plot on the lower green plots takes 10,000,000 to expand to. These costs are serious obstacles early in the game. I think most players will not expand to the Treent plot until they are around level 35-45 or so. I recall that it took me a long time to get enough coins to expand to it (I think I was level 35 or so when I could finally do that).
This is the post with expansion costs per plot:
https://forums.storm8.com/showthread....=1#post1092567
That post was made by Zenobia, who sadly left in May of this year. The drawing is incomplete, but should cover enough ground for about a year's worth of expansion costs.
I did keep track here and there in screenshots and some posts how much the recently added new plots cost, but I don't have it all in a single image...