What lovely ponies! Looking through these, the first thing you are going to want to do is identify the ponies. There are lots of ways to do so, though my personal favorite is strawberryreef.com
It seems like you've got mostly generation 1 ponies, so that's a good place to start.
Once you know which pony you've got, you should assess its condition. Some things that can bring down value are haircuts, scuffs on the paint, deformations to the body, etc.
A popular way to gauge price is to go on Ebay, type in the pony's name (for example "MLP G1 Peachy") and then look at the "sold" listings. This is a good way to tell what people are willing to pay for a particular pony right now.
Taking a quick glance over the picture, from G1 I see Peachy, Sunbeam, Firefly, Sundance, Sunlight, Starshine, Sparkler, a bunch of baby ponies, Angel, Milky Way, Cherry Treats, Cranberry Muffins, Boysenberry Pie, Brilliant Bloom, Twinkler, Sweet Pop, Magic Star, Wind Whistler, North Star, Zig Zag, and a whole lot more! I hope that can get you started.