Kit cost break down is to do a complete front end, new 11.75 rotors, bearings, seals, hoses, then the specialized caliper adapters and, of course, the calipers. So the price differential is purely due to the adapter and caliper pricing. There is a fairly large spread between used and new Viper parts, hence the large difference at that end of the spectrum. I'm restricting things to 11.75 because of the the 15" wheels I'm using. If I'd step up to 17", then I'd just get a 13" rotor kit and be done with it, but I already have the wheels and tires and don't want to dump a couple grand on new ones just to go dump another couple of grand on even bigger brakes.
Wilwood and Viper kits are AR Engineering pieces. Very well thought out and functional. There is no kit for corvette parts, unless you count Baer. Nor is there anything using Mustang calipers out there either. I just threw that in there to spike your melon. Although there is a rumor that Kore3, OEM supplier for Corvettes, is working on Ford and Mopar kits for C5 and C6 binders. I suppose a seperate, yet expensive option would be to entirely change spindles to fabricated units and use 12.12 rotors with Nascar Cup type 6 piston calipers, but talk about buck$$$!!
Pros/Cons
Wilwood; race proven design, light weight-10# per wheel weight reduction, four piston, fixed bridge design with high clamping force, consistent sized (1.75) pistons for variety of applications so may require balance valve or change in rear wheel cylinders, no dust seals, requires regular inspections, pads only available from Wilwood distributors, very racey looking, only available in black at this price, but for $150 more, can be ordered in red.
Viper; race and street proven design, lighter than stock-about 5-7# reduction from original, four piston fixed bridge design with very high clamping force, offset sized pistons (38 and 42 mm) to maximize leading/trailing clamping forces, originally designed for heavy vehicle with high output, reliable street use for many years with no problems, pads available almost any where, just plain bad mo fo looking, originally only available in black with RT10 or Viper printed on them, but rebuilds are available in any color-black-red-silver-yellow-etc also with Viper printed on them for no additional money.
Info on adapter kits;
http://www.arengineering.com/caliper_menu/calipermenu.html