I know that Michael's estate in GF2 was filmed at the home of former industrialist Henry Kaiser on Lake Tahoe. It is now a condominium complex called Fleur-de-Lac Estates, and the townhouses go for about $5 million. Here's a description from a realtor's website:

Fleur De Lac – 22 different spectacular condominium homes were created from the old Kaiser Estate (Godfather II was filmed here). Unsurpassed amenities include its’ own harbor with boat slips, swimming pool complex, tennis courts, etc…. A private gated community.