Actually, that's probably about the right price OP is asking, given their base in-store price.
Mane-6, plus Trixie at 10$ a piece = 70$
Dərpy, which was only so far released at Easter time, easily sells on eBay for 15$-25$ alone.
The Princesses range for about 25$-40$ a piece (Celestia seems to sell for the most)
Tallying that, they're worth about 160$-200$ Easy, the problem here though is most people have some of the plushes already, so looking for someone willing to splurge on a whole set is going to limit the possible clientele.
My best sugestion to OP would be that if this lot doesn't sell the first time around, try breaking it down to smaller lots for more buyers interest. (Maybe like a Mane-6 set, Trixie/Dərpy set, and the Princesses as a set. )