More like 400-450,you must have a different engine to thousands of others.
I was going to say that.
I find it's just under half the figure I put in(x10), if you know what I mean.
That's how I work it out.
eg:  £10 just under 50 miles.
       £20 just under 100 miles.
       £50 just under 250 miles. 
So for £100 I'd expect just under 500 miles, probably 430ish.
I reckon if you were mainly motorway at 70mph in 6th  you'd get miles more though.
Mine's the  2.0, 115bhp model by the way.