Picking a sub

I have a 600 watt Amp. What is a good sub to put with it without breaking the bank?

Hi Jerry, welcome here!

You will get more replies and better help if you give us a little more information.

For example, what car? Where do you want to put the subwoofer box? How big of a box are you willing to have? What does breaking the bank mean, to you? What amplifier do you have? Do you want sound quality, or do you want as loud as possible?