Hi there!
Well, I have seen the buggy sell complete from anywhere between $70-$150. The important question is, would it be worth $135 to you? There are many sought after sets in the MLP line, if this is one of your favorites why not go for it. Personally I recommend against buying ponies just because they are sought after or rare, or to have something "brag worthy", Instead buying the ones that you'd really love to have and enjoy.
Sometimes sets fall in and out of favour, or prices can go down due to someone finding old store stock. MLP "Mommy Charms" are an example. They used to be highly sought after, valuable, and fairly HTF they now sell for less then a third of what they used to and go unsold often.
Are all the pieces present with the set?
Buggy: basket, wheels, handle, umbrella on pole, heart topper
Accessories:
2 white with silver threading lace trim pieces.
1 metallic fuschia ribbon (ties to heart topper)
1 White with silver floral mesh bow (for baby sparkle)
1 pink fuzzy blanket
1 Turquoise Baby Dish
1 Pink spoon
1 Turquoise Sippy Cup
1 Shooting Star hair clip
1 Duckie Comb (deep purple or a bright purple/pink)