How do I price my horse?

You should be able to find someone to lease her. Look specifically for a kid who is growing out of a pony, cuz she sounds like a great starter horse. At age 17, people would probably find leasing to be beneficial because they're not going to be responsible for her 5-10 years from now in her "golden" years. Keep looking around, hang flyers in tack shops and feed stores. You'll find someone who fits your criteria and wants to lease your horse. And if you're really having trouble, waive the lease fee and just have them pay expenses. Just be sure to make up a written contract regarding care, health, etc.