On a KDX, they would be well worth the money. But you also may have to consider stiffer springs, depending on your weight.
As for installing them yourself, its not to hard, if you have good mechanical skills, and a normal assortment of tools. I don't think anything special on those forks are required. You will need a digital micrometer and an inch pound torque wrench though.
As for cost, RT charges $100 labor, on top of the kit. You may want to find a Race Tech Center in your area, and price them out. Or even if you have a good shop in your area, see if they can install them, and price them out.
Good luck.