Is this 99' Grand Cherokee any good for 2900?

You will have to drive it. Watch for late shift points (42RE), growl from frt and rear Dana diffs. It should drive quiet, straight and strong. Bumps, braking and cornering should also be quiet and controlled. Do a walkaround. Open and close each door. Look for and paint overspray or accident tell-tales. Make sure that absolutely everything works before signing anything. Google the seller for customer concerns.
Remember that it is a 13 year old vehicle with 150K and that it will probably need some work. At this age and mileage, everything has to be considered maintenance.

I just bought a 04, so in addition to what ImperialCrown said make sure if the HVAC controls are automatic make sure it works. Blend doors have a tendency to break leaving you with no heat. there is a easy fix for this that doesn't require tearing the dash out. I havent had this problem since I have only had mine for a month, it's all over the internet. If everything seems to work ok that seems like a fair price, once over the 100k mark the value nose dives somewhat.