http://www.goodmart.com/products/85730.htm
Gets kind of pricey and is non-adjustable.
sammy appears to be descended from Michelangelo, so your jig saw results may vary.
If you are clutzy (like me) with a jig saw, you can make nice round holes using a router + circle jig:
Changing Rear Door Speakrs in CC w/ RF
Unlike a hole saw, this allows you to make many different sizes of holes.
This generates lots of dust, so if you don't have a place to work, you could probably have them made at a local cabinet shop for not too much $. My kid's high school has an extremely well-equipped wood shop, so you might check out your local high school. Might be a nice little project for some kid.