I think both brands have a series of forks which start from about £350 and increase to about £600. So for RockShox you have Reba, Revelation, Boxxer and Sid at the top of their respective categories (Anything/freeride/downhill/xc) and the cheaper Tora and Sektor are basically cheaper versions of the Reba and Revelation.
I'm not sure about Fox, but I'm sure it's pretty much the same, they will probably have one fork in each category and then various models of the same fork which have better specs.