Once you determine your desired gear ratio your priority should be to find the best jeep gear installer in your area and have that shop supply all of the parts. The better gear shops will refuse to install customer supplied parts. Even the shops that will install customer supplied parts will refuse to warranty the labor if it turns out the parts are defective or the cause of a failure.
Supplying your own parts is a false economy unless you are doing the work yourself, particularly since the U.S. Supreme Court in South Dakoka v. Wayfair, Inc. eliminated sales tax avoidance on Internet purchases .
As for cost, an average for parts and labor for a re-gear by a good shop is $1,600 +/-. How much the +/- works out to be will depend on the particular gears you buy, the shop labor rate, and a myriad of other factors.