differences between LS and Z34

I might be buying a monte carlo LS, and i was wondering what the differences are between the LS and Z34.

I know that the Z34 has a bigger engine (3.8L if im not mistaken) and the LS has the 3.1L (once again, im pretty sure)

Also, can someone give me a quote on about how much this car is worth:

99 monte carlo LS, with 30,000 miles, it is in very good condition, and garage kept. It has the wheels with the really thick spokes.. if you could even call it that, they look like non-finished aluminum. It has a tape deck, and regular cloth interior.

Im just looking for a ballpark estimate.

thanks

Go to www.kbb.com. For the estimate