re-gasketing is literally a $25 job. If you only need to do one diff, maybe a $15 job. ~$10-$20 in gear oil(just a guess at what 2-4 quarts of gear oil will cost you) and a $5 tube of permatex gasket maker. The new oil resistant stuff is supposed to be awesome otherwise use gray.
I dont know on the new gen diffs if I would worry about swapping to lube lockers(im not personally going to do them). Not like you have to open up the diffs a bunch to drain them, unless of course your diff skids cover up the access to the drain, then yea, I could see lube lockers being a worth while investment. Although at ~$20 a piece($40 total), you can buy enough permatex gasket maker to re-seal both your axle housing's ~8 times each, which is probably double the amount most people would change gear oil in the life of a Jeep. If you are somebody that changes gear oil after every wheeling trip(some people do due to water crossing a lot which tends to let water seep into the front diff, not so much the rear) than lube lockers might be a good investment.
drain diff from drain plug. Remove cover. Clean mounting flanges of old sealant. Re-apply new sealant. Replace diff cover. Torque bolts in a star sequence like you are doing tires. Wait a few hours for gasket material to dry. Re-fill with new fluid.
