My DH's parents have, in my opinion, unrealistic expectations about how often we see them. I won't say what they expect vs what we want, because I don't want to bias you.
If you lived two hours away from a set of grandparents, how often would you visit? If the age of our kid matters, she's about two years old.
EDIT: this is for total times LO would see the grandparents, regardless of whether they come to you or you come to them. So if you think it's only fair the grandparents drive down once a month and you drive to see them once a month, you should choose the every other week answer.