Hello! First, let me say I don't know much about the baby pony outfits--I know the pocket pals are often somewhat sought after but I doubt they're very expensive. What you have left is *very* common pony wear. Pony wear itself tends to be ignored by most collectors, so the demand is low while the supply is high. Sweet Dreams and Great Skates may be the two most common pony wear outfits. Since you'll be at the fair, you may be able to sell them for $3/each since someone can just pick them up (no shipping). At least they are complete (the Great Skates headband is easily lost). The Flashprance and Pom Pom Pony bits are <$1 each.
Common combs and brushes usually go for $1-3 based on just how common they are. Ribbons are usually $2 if they are in good condition, maybe $3, maybe a tad more if they are less usual colors.
If you're selling the dark green, yellow, or purple shooting star/comb sets that came with Rainbow Ponies, let me know! I'm not going to the fair but I'd love to buy them!