I lived in MK for years and did my training there and you would struggle to get any closer unless it was in the middle. Its just a few minutes drive from MK, although it is a big place as you no doubt know so it depends which side you are driving from.
Traffic is never a problem there so even if you were driving from as far away as Crownhill at the far side I cant see it taking more than 15 minutes to get there. If you live at the nearside of MK it is minutes.
I flew in there to see some friends a few weeks ago and paid a fairly steep landing fee although I am sure you can get deals on that.