My family and I just got back from a trip to Niseko (skiing) and Tokyo (city thing). We were lucky enough to be referred to local guide for our Tokyo sojourn from friends who were expats there for a while. The cost for a private customized tour was 25,000 JPY (approx 210 USD) lasting about 9 hours. We loved her. (I have not quite 7 year old twins).
PM me if you would like me to send you her contact info as I am not sure what the rules are for posting websites or email ID's.