Science Sound/Kinetic Sculpture Project

What I am planning to do is to have a mini tennis match with sound effects. There will be two ping-pong paddles on either side of a miniature tennis court hitting a ball back and forth (I'm still sorting out how to do that). Using the arduino board and a speaker I 'd like it so that when the ball hits one paddle, it will make the sound of a Sharapova tennis grunt, and the other one will make an Azarenka grunt. My question is I want a good way to control when either grunt takes place, either with a sensor or just timing. This is also my first time doing anything with arduino besides just making lets flash with timing so if you could also include a basic programming idea for it too that would be great, but not necessary. Thank you! I also have a fairly small budget.

You can try some sort of pressure or touch sensor mounted on each paddle.

HungerSymons: miniature tennis court hitting a ball back and forth (I'm still sorting out how to do that).

Automating that with a ball in free flight would be extremely difficult. If the ball is tethered in some way, it becomes much easier. In that case you might also be able to use the ball+tether to complete a circuit through the paddle and use that to trigger your sound output.