At 86,000 miles I have used about 1,791 gallons of gasoline with my Prius. Compared to 4,095 I would have used with my old Subaru Legacy or Audi A4. That is a savings of 2,304 gallons of gasoline or about $6,912 in fuel savings at $3.00 per gallon (Prius also takes regular and my others took premium). Plus, the Prius was less expensive to purchase and maintain.  Yes, I do think it was a good investment and at 86,000 miles I have had only one mechanical issue.

Updated:  9/25/2013

Over 105,000 miles and still going strong.  I put new tires and new struts on.  The brakes were still at 35% during the last inspection.  (Updated post)