Ball Joints
 

There's 4 right? Where's the best place to get them. (cost/quality)

wait whats the differnece betweeen tie rod ends and ball joints

Yes, there's 4. Some call them tie rod ends, some call them steering ball joints. Of the four, there are three alike threaded, one opposite thread. D.A.P. sells a kit of all 4, and they are greasable, and only $70

There's actually 5 on a D1. Two each on the track rod and drag link, and one at the upper A-Arm mount in the rear, though that's a different type, but should still be inspected periodically.
The ones DAP sells are usually greasable.
If the ones you get have nyloc nuts, before you install them find a plain nut that's the same thread. Use the plain nut to tighten them up, then remove it and install the nyloc. Otherwise the nyloc will just cause the taper to spin and you can't get them tight.
If they are castellated nuts then you can skip the above.

Good point about the rear ball joint... everyone overlooks them...

Tom is a wealth of knowledge on these things. I learn something from him quite often. Thanks for the information.

Ready to buy mine now? whats DAP link?

Can the rear ball joint be replaced while the vehicle is on the ground or does it have to be on a lift

No. It has to be supported.