New Stereo/CD for 1999 Jeep Grand Cherokee?

I have a 1999 Jeep Grand Cherokee. Right now, it has a 12-CD changer in the back end (not an in-dash CD player), but it doesn't work, and the speakers are going out. I'd like to replace the system with new speakers, and in-dash single CD player, and replace the 12-disk in the back. Wondering about how much I should expect to pay, and how I go about asking for what I want so I don't sound like an idiot. THANKS!