Is there any inexpensive options for a peep sight that will mount on the dovetail rail of a 22 or pellet gun? My stepson wants to get more experience with a peep as that is what he will be using on the muzzy this fall. We will have time for him to shoot the muzzy but he wants to be proactive about getting better with shooting and would like to get one to put on his pellet gun so he can practice when we cant go shooting. I was hoping for $20 or less. I saw a Williams one for $35 + S&H but was hoping if there were any more inexpensive options.