If you get an the 00-04 model xterra, a good lift (3 inches) will run you in the $900 range, an upgraded steering kit will run you around $500. That will allow 33's. If you want, you can also do a 3 inch body lift for around $250. The only locker choice is an ARB air locker, or if you have the open dif in the back (not the LSD), you can get a lockright.

I would wait for the 05 Off Road, comes with 31's and a locker. Calmini has already been working on the lift... so you will be able to fit larger tires.