I'm about to buy an older home that has all ungrounded outlets except for an addition off the kitchen. I talked with the homes inspector and he says that it's almost without question that the kitchen at the very least will need grounded outlets. I'm weighing my options now. I know all electricians are different but do you have any ideas of what the cost would be to do one room and then for the whole home. That would include the kitchen, dining room, living room, two bedrooms and a bathroom.

The electric met the code at the time the house was built. There is no requirement to upgrade that short of major renovations. You may wish to do it, but it is not a requirement. Only way to determine cost will be to have electrician give estimate.