Push up bar and ball - $15 (La Crescenta)

SKLZ Core Push Up bar and unstable ball.
Used, but in excellent condition.
I haven't used these in years, but used to be part of a push-up club that challenged us to do more difficult workouts.
They make pushups SO much harder, and the gains you'll see are impressive.
The price is for both.
With the ball, put one or both hands on it, then do standard pushups - the instability will really work your shoulders.
With the bar, put a baseball or some other hard ball (I used a dog toy) underneath it, and then follow the exercises on the front to work your shoulders and core.
Or use it straight off the ground to build up better forearm strength.