On IAR's EWARM package, what is the difference between the built-in MISRA C checker and CSTAT's MISRA C checker?
I asked the same question to IAR last winter. "Do I need to buy C-STAT for MISRA-C checks?". Rough translation to English from my correspondence with them:

Yes, MISRA-C checks are done by C-STAT. It is integrated inside the IDE, so you need to buy an EWARM version with a C-STAT license.

To be sure, ask IAR sales. You'll want to ask them about pricing anyway.

However, you need to know which MISRA-C you are using. If you don't, you shouldn't be doing this tool purchase. IAR supports both MISRA-C:2012 and MISRA-C:2004.