Iron horse bit: price?

I was downtown taking pictures today and decided to step into an antique shop. I am starting to collect antique horse bits and the shop owner showed me one that he believes is made of cast iron (looked and felt like it) and he thought it could be old enough to have been used in the USA cavalry. He said he would sell it to me for $20. I'm going back tomorrow to buy it (didn't have any money on me and he said he would hold it for me). Just was curious how much it could possibly be worth. It is a cast iron correction horse bit.