It's hard to say as only a few have sold recently on eBay. 2 out of the 3 sold for a best offer so we can't see what they actually sold for, but 3rd sold for 60 +shipping. It used to sell for over 100 so I'd say the price has probably dropped quite a bit although it could just be time of year.
If you are going to sell I wouldn't take less than 60-75 as I believe 2 fillies (Silver Spoon & Twist-a-loo) are exclusive to this set & I think the retail price was 30 at Target.