I saw this fan http://www.coolerguys.com/840556017059.html
Its 92mm with 56db(its loud) but it has 119cfm
Are you going to be using a fan controller? If so you can turn it down so its not so loud.
After you get your fan and grill, Go into your shop and see if you have a hole saw the rite size, If you don't have the rite size, you should use the roto zip with a cutoff wheel or a jigsaw. Just use what you have. Any of these tools will do the job nicely
If you take your time when you do it, Your finished product will turn out good. Besides your grill will cover it up anyway