Welcome to GS, Andrew. (I just sent you a message from metroMPG.com suggesting you check this site out - guess I was a bit late
Metros are neat, sure, but as has been pointed out, there are other options.
If you're doing mostly highway driving, a Civic VX will kick the Metro's butt (lean burn at low load cruise). A Civic CX would be another car I'd consider looking at. (clencher: you forgot to add "Festiva" to the Ford list.)
If you're doing mostly in town driving, the Metro's lighter weight and low-powered engine make it pretty hard to beat (particularly when you start throwing driving technique at it).
Have you thought about going diesel? Find an old Golf and you could completely kick the oil barons out of the picture - do a greasecar conversion.
But, if you've got your heart set on getting a Metro (I was), first: realize that with "normal" driving technique, you'll have a difficult time reaching the (old) EPA mpg estimates. And be patient. Something will turn up. I spent months looking for the two '98 versions I bought, and most I saw were overpriced too.
Anyway, whatever you decide, good luck and keep us posted.