The price of the complete 5 valve solenoid manifold stack assembly (p/n 641205) was $323.91 plus applicable tax & shipping when I bought one on 4/19/2010. The individual coils/valves (p/n 641929) were $32.59 each if you want to order spares.
Depending on the vintage of your coach, replacing the whole manifold assembly can be the easiest way to fix failed solenoids/coils/valves
or be a royal PITA because of the configuration and orientation of the current manifold block. On my coach (1995 chassis), installing the new manifold stack intact would have required completely reorienting the air connections and the electrical connections to mount it to the steering bay bulkhead where it already resided. After much head scratching and gnashing of teeth, we just decided to swap the individual coils/solenoid valves from the old and new manifolds. The end result was the same and I didn't have to figure out how to reroute the air line connections and electrical connections to accomodate the different configuration of the updated part that is now being sold/shipped.
Had I known then what I know now, I would have saved myself a few bucks and just bought 5 of the individual coils/solenoid valves for $32.59 each ($162.95 total instead of $323.91). Live and learn, eh? "You have to pay to play!"