The only Sprinters within the price range you mention would be the 2002-2006 T1N models. All such US models had the Inline-5 Turbo Diesel engine and 5 speed automatic transmission. Fuel mileage between 20-25 mpg can be expected and varies due to speed and city/hwy driving conditions. Fuel mileage differences between the shorter 140" wheelbase and longer 158" wheelbase model will be minor, perhaps one MPG or so.
We have the 140" 2006 high top, but given the number of people, dogs and bikes you're looking to carry the longer 158" is probably needed.
