Ok firstly here is the asda fuel link http://your.asda.com/fuel-prices lets work on a figure of £1.38 a litre
5 litres of unleaded (not premium ) would = £6:90 (as close as i can get to £7)
Your tank holds 17 (seventeen) litres so given a generous 3 litres for reserve that leaves you 9 litres short of a full tank !
5 litres on a 175bhp 2004 zx10 and lets say a limp wristed 35mpg would get you about 40 miles
manufacturers can exaggerate tank capacities just like bhp and dry/wet weight,im telling you what i spend from reserve light coming on to the pump tripping off and its always £7 whats the point in me telling porkie pies?
@the op you can buy a tax exempt/reduced car like a toyota aego,the tax on those is free or something like £20 i think
someone else on here ownes a zx10 maybe they can chime in