Hmm they are pretty expensive. Cashel and reinsman are the one I've been seeing, but those are $95-105. Tuffy used to have one, but they seem to be discontinued everywhere. Did you try looking for a used one? I had seen one on craigslist for $75 near pittsburgh pa... but can't seem to find it now... sorry I'm not too much help!
Your mare is very cute by the way, I love how fuzzy she is, she looks like she'd be great to jump on bareback