A Crown Car, Town Vic or Marquis De Sade are all good choices. Excellent engines, transmissions and rear ends. Great MPGs, lots of options. And best of all nice used examples dont go for much at all.
Rest assured you will find the majority have been senior owned and operated, which is usually a good thing.
Here's my beater. 1988 Bronco II with 4x4. I paid $550 for it but all together I have about $2000 into it. It is very reliable and gets decent mileage but you don't want one with the original 2.9L V6 engine. They are absolute junk. I put a 4.0L V6 out of a 94 Explorer in it. Of course, it has been painted and has had a few add ons but for $2000 I couldn't be happier.