I am a big fan of RCD lifts myself, with Rancho a close 2nd. I would not really consider any other lift in the 6" and lower range. The main difference between the Rancho and RCD is the crossmember for the front differential. Rancho uses a one piece crossmember and RCD uses a two piece crossmember. The two piece crossmember allow the frame to flex when placed under pressure (articulation situations).
Rumor has it that the designer of RCD used to be the top designed for Rancho, however Rancho would not let him do what he wanted, hence RCD was started.
In actual lift difference, RCD will put the truck about 1" or 1.5" higher than the Rancho kit. Regardless of what kit is used, the Bilstein shocks are the way to go, they come standard with the RCD kit. Even if you opt for the Rancho kit, get the Bilstein shocks. Do not get the Rancho shocks (5000, 9000, etc..), Edelbrock shock, etc....
As far as price is concerned, you should be able to get a RCD kit installed for about $2400. If you shop around, you can probably get one for about $2000-$2200. Also, don't bother doing dual shocks as the Bilstein are specifically engineered for each vehicle (which is one of the reason why they are so good). Rancho uses the same shock and just puts different ends on them for whichever vehicle they are put on.
If you have any more questions or need more info feel free to ask or send me an email.