I voted 190D turbo before I read the OP. A 124 diesel with a 5-speed should get you into the mid 30's mpg highway with everything working right and normal driving style. Manual 190D's (turbo or not) can get a bit more, but not enough to make me change cars if I already have something I'm happy with. Come spring you might want to consider using a motorcycle on nice days. My old 250 got 55 mpg and I rode it like I stole it.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.