Why $400 more for a solid roller cam head? The only thing they'd likely change is the springs and they sure don't cost $400 more for a solid cam spring versus a hydraulic cam.
Hydraulic flat tappet 1.460 springs .650" max lift 1979.00
Hydraulic roller 1.550 springs .680" max lift 1999.00
Hydraulic roller 1.550 springs and titanium retainers 2199.00
And solid roller 1.560 springs and titanium retainers 2199.00
The difference is in the springs, guides and retainers I guess.