I think you can get good Pellet gun at wally world for about 80-100 USD
I'll never forget when friend of mine killed a mouse w/ a BBgun.
Small hole in wall near the corner of the garage, mouse seen entering/exiting from hole to dogfood bag. Place a teaspoon of PeanutButter 2" outside the hole, set chair bout 6' away backwards so you can rest barrel of BBgun on chairback, wait less than 3 minutes, mouse exits hole and heads strait to PeanutButter, Mouse killed on first shot. Good Times!:D