I think the ultimate "sleeper" hypermiler car is the SOHC 5spd 95-99 Neons, these are rated in Canada at 43.5 MPG highway. This is
better than a 2000 Echo for example or any of the normal Civics or Corollas of the late 90's or newer.
With the Neon's bad reputation, probably you can find ones with low miles for well under $1500.
www.neons.org has more information on these cars than you will ever need. I'd say they are not a car for people who get bothered by little problems or can't fix little issues. The frameless windows whistle at over 60mph, etc. But the interior of my 95 rattles less than my friends 2003 Echo so they are not totally hopeless either. The wannabe racers all go for the DOHC versions but the SOHC ones will have Honda civic owners amazed how hard a 4 banger can pull at 2000rpm and still do OK at redline. If you are into engines, these ones like to rev and are import smooth doing it.
Ian