For the first question... Never hurts to re-pack bearings anytime...
Also I've found the body mounts (bushings, bolts and brackets) have a lot to do with on road stability while driving... But if it is just free play itself while sitting, try to be more specific... I assume you mean free play in the wheel turning back and forth? That steering post i posted is awesome info... Check it through for all kinds of ideas of stuff to check.
As far as ball park on (i'm assuming) disc brake conversion, probably around 600 - 1200 depending on what kit you want and without ever doing it myself, just researching for my front differential, there are a lot of little things to consider.
I am not familiar with your year at all, so not sure really what is a true actual ball park figure. Also depends how you want to do it. Want to go search for parts through the junkyard, and get cheaper, but not a full Kit? Or want to order a full kit of all new components and slap it all on there?
Check out what type diff you have, then start checking on our sponsors websites for pricing. Need help post what diff you have, people can start helping better from there.
~ JR