If your looking to do the 5 lug/disk brake swap cheap, buy a V6 rear complete and strip the axles and brakes, then take all your parts and put them back on the V6 housing to sell in the paper or wherever (7.5" 4 lug open $50). Net cost will usualy be $150 or less. ($150-$200 is typical for a V6 rear complete)
You may already know this, but in case you don't: The V6 brakes are the same as GT and the axles in a 7.5" are the same as an 8.8"