Answer
Strange question - try eBay.
Answer
I'm not sure how much it will sell for or who would buy it. If you're going to be able to sell it, the Interneti d probably the most likely. But if you can't sell it, you could try donating it to Locks to Love. They're a non-for-prfit orgganization who makes wigs from human hair to give to kids who lost their hair for medical reasons. (One example of this is cancer). I donated 15 inches of my curly brown hair. If you haven't got it cut yet, you can try going to their website and looking at the list of places that will cut your hair for free and send it in for you. (Its quite a long list).
Buddysharp.com answers: I have been buying hair for over 27yrs. As one of the leading Extension Artists in America I will tell you how it is priced. 12" hair will sell for wholesale in the range of $25 an ounce the average ponytail is about 4 maybe 5 ounces. You can do the math. Thanks Buddy 214 535 7849