Not really MZ.
ARB Locker - ~$700US (in the contigious 48)
ARB Compact Compressor (all you really need to run the locker) - $140
Shipping - $60
Now....installation is where they get you, however, if you pull your 3rd and bring them the 3rd and the ARB and say, hey, put this in here, you can walk out with it for about $2-300 or so.
Then install the compressor and air lines yourself (figure on about 5-6 hours for running the wires and switches and what not), put the 3rd back in the truck, hook up the locker, fill the diff with oil and badabing badaboom.
Hell, you could even pick up an extra 3rd from a junkyard for about $2-300 and have the shop install the locker in that, and then just swap 3rds and sell off the other one. Any 3rd with the same spline count will work.
Now, if you have the shop pull the 3rd and put it back in your truck, you're looking at about $550-600 for that job.
It can be done for a LOT less than $2,000 but you have to want it to be done for less than 2k. Having a shop install everything will probably run you about $2k for a rear locker and $3500 for Front and Rear.
Or....instead of using the ARB compressor, you only need a compressor that is capable of spitting out bursts of 90 psi ever several minutes....so the Viair 100C or 100H would work, as long as you don't plan on using that compressor to fill tires.
http://cgi.ebay.com/ebaymotors/Viair-100C-...067273725QQrdZ1