Believe it or not if your not too against it I would look to buy one off of EBAY. I have bought many many items off that site and have been pleased so far. If your anything like me and your always looking to save a few dollars than its definitely worth looking in to. I have never seen a new locker for less than $400. As for a locker being the only way to lock your wheels, the next best thing is a Ford Traction Lock differential. They use clutches and springs to positively lock your rear tires together. I currently run one in my Cougar and it runs mid 7's in the 1/8 mile. I highly recommend them for street driving. You can get then for $200 or less pretty regular.
Not from Nascar, from one of the teams. I have seen a website for Jack Roush's used parts but don't know the url. They had every sort of rear end part on there from cases to gears, all used in one practice or one race and at about half retail price. Any one know the net address?
The only problem is that the NASCAR teams seem to all use 31-spline axles, and almost all of our Cats are 28s. 28 spline lockers are a bit harder to find! I got mine (28 spline) off eBay, with only 50 miles on it, for substantially less than the MSRP.
Mine is powertrax performance locker, and you get two types of springs, "drag" and "Street". I have installed the streetspings, and they give only a silence click in curbes, but lock immidiatly when i floor it. I guess if you use dragsprings, it will be allot of difficult to cruise. They told me that detroit lockers make allot of noise...