That Crown Vic should get better mileage than the Tempest/LeMans would. The CV should get around 23 mpg highway/16 city, and average around 19 mpg (according to Fuel Economy
I was going by the price guide when stating there wasn't a LeMans four door. I just looked at a few other sources and yes, there should be a LeMans four door model for 65. It's the top trim for the Tempest body (Pontiac GM A-body). That might add another $300-500 to the pricing, but no where near the LeMans two door models.