Yaris...
a definition of inexpensive may help. I have a '97 cavalier that gets mid 30s in the summer (and as much as 37-38 if I work hard at it) that I paid $2k for.
That being said, I gave $12k for my yaris with around 18,000 miles on it and it got 41mpg right out of the box. That has gone down as I have done some performancy stuff to it.