Sl1, sc1, or Sw1 is the best bet. Yes it was discontinued in 2002, however this is an easy car to work on, reliable, and doesnt have to be brought to a dealer to get it fixed. I got 2 s_1's both achieving around 38mpg with veryyy aggressive driving. My '02 got 42mpg with the a/c on, doing 70 - 75mph down to Florida on '95. (the '02 has 178k miles on it also, a teenager in the s-series world

).
Any s-series matched with a good set of tires is a great economy car. My sl2 DOHC gets 34 on the highway.
I have gotten all my s-series cars under 4K. Can you buy a new car at the dealer at that price??? Even adding on any maintenance bills i still wont even reach a dealer price for the aura, ion, or any other saturn haha