Plan on $1100-1200 to regear including all parts & labor. To know what ratio you have, jack up your rear end, place the t-case into Neutral, and then count the number of times the rear driveshaft rotates as you rotate one of the rear tires precisely two times. If the driveshaft rotates 3 (3.07) times, you have 3.07. If it rotates nearly 4 (3.73) times, you have 3.73.
If your rear axle has a limited slip differential in it, just rotate the rear tire once instead of twice. You can tell if your rear axle has a limited slip differential in it by watching the other tire. If it rotates the same direction, that indicates the presence of a LSD so just rotate the tire once. If the other tire spins in the opposite direction, you don't have a limited slip differential (or the clutch pack in the LSD is worn out) so rotate the tire twice while watching the number of times the rear driveshaft rotates.