SSBC Rear Disc Brake Conversion Kit difference?

got the links for where your looking?. the one i found was almost $1000! what are you installing them on?

These should be the links.
Mopar 8.75/9.75 Rear axle Disc Brake conversion Kit - A155

Rear Disc Brake Conversion Kit - Mopar 8-3/4 and 9-3/4" rear axles - 1 (Single) Piston - 10.5 inch rotors - W155