Tercel's are pretty cheap, and they're easy to maintain. You should be able to pick up a manual Tercel for less than $1k, I think I paid $900 for mine with 130k miles about 4 years ago. They're not the most aerodynamic though - .36 cd.
Corolla's usually have a lower cd, but they're usually a bigger engine, and weigh more. The Tercel is less than 2000 lbs stock, I think the '93-'97 Corolla's come in at somewhere around 2400lbs.
Personally, for pure MPG driving, I would go for a Metro. Although the CRX's just look so cool.
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