ML320 CDI vs. Bluetec

ML320 CDI vs. Bluetec

I'm considering buying a Used but Certified ML 320 CDI or Bluetec. I'm looking at a 2008 to 2011 at our local dealership. I have two questions.

First, I'm being told that I can expect to get 32 MPG when at highway speeds. Is this accurate?

Second are the maintenance dollars. It is my understanding that the Bluetec costs more to maintain than the CDI. Is this correct? What can I expect to spend annually on maintenance?

I'll look forward to hearing your responses.