I'm currently getting 28.5 average from my 350Z, 32 from my Golf VR6. Driving carefully obviously and treating it as a bit of a challenge.
Coming back from the Gower (S Wales to Hinckley) the other month I average 40 mpg in the VR6, yes 40!
Main reason is not the cost saving, just a challenge to relieve the boredom of normal driving and speed cameras.