Hello @Sreenath G
American specs are ok if you can be sure of the accident history and the car is in decent condition. The Americans don't dune bash like us. Most of them would overland which doesn't damage the car as much.
Do note that US Xterras also come in 2WD models as well, so you need to get a "Pro 4X" model which is the Offroad version we have here. If not, just jump in and look for the 4H, 4L knob. A 2WD X is good only for pulling donuts.
American Xterra's electronics are the same as the GCC ones. Anyway, you will install a kill switch for traction and ABS before entering the desert.
Check the radiator and the cooling system thoroughly. American specs have a history of SMOD. Google it. If you see any traces of SMOD, walk away, not worth the headache.
Regarding the budget to get it desert ready - You will have to change all fluids(engine, trans, transfer case, diff) and then drive the car to see other issues. The X has a tendency to hide issues and expose them one at a time in regular intervals
2008 X for 12K seems too shady. And if has been abused, not worth the risk and 8K might not fix it. Again, it depends on the condition of the car. Don't worry too much about the interior, thats inexpensive to fix, the mechanical part is what you need to focus on.
Thank you!