If I understand correctly you have the following, plus a cRio I chassis.
- qty 2 - 9201 - analog input
- qty 2 - 9403 - digital I/O
- qty 1 - 9472 - digital sourcing ( solenoid base driver )
If you want to have two control systems, by getting a chassis, and moving a 9201 and 9403, thence comes the questions, a'ha !!
Looking at the full retail price of the NI 9472, it is $ 99.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/208822
The only way to find out if there is a discounted price structure is to contact NI at the same phone number that you call to get the cRio II. It would not surprise me if there is not a discount price for the single item.
If you have enough cRio chassis of any vintage I don't see enough advantage to warrant spending the money if it isn't in the budget.