I went through all this before I bought mine - honestly don't think about it too hard. You arrive at work smiling and you arrive home from work smiling - it is priceless!
But for the record -the above figures sound right, I get about 25mpg with a mix of driving/roads. Mine is a March 06 so is £245 to tax, post march '06 I think you are lookin at over £400. Make sure you know what the usual 350 niggles are and if you want peace of mind get the car checked out before you buy it. As its a Nissan not much should go wrong.
I just so happen to know where you can get a march 06 mint car for £13,800