How much is a juner air gun?

Are you asking about a Webley & Scott Junior Air Gun? If so then, if you can find one of the New model Junior's, made between 1945-1973 In Excellent condition, it will cost around $350. The price drops from there depending on the condition of the pistol. If it is the earlier model the price changes completely. You need to give more information if you want an estimate of value.