Feel free to post a picture of your find and others will give you their opinion. Without seeing it, the likely condition would not warrant an appraisal. With a steel planchet exposed to the elements, they are quick to corrode. Now, if the coin was properly stored over the years and had only recently been found, then it might warrant a numismatic premium if it is in mint state. If it has been circulated but still corrosion free, then it is worth only a slight premium.