Dean
Fuel will not be a killer if you price up the work right.
To me fuel is quite cheap at about £1.43 per litre - its much cheaper than many bottled waters for sale and certainly a lot cheaper than 568 ml of beer at my local pub which is circa £3
Most new businesses look at turnover rather than profit, it's far better to turnover 100 grand and make 90 grand profit than say turnover 200 grand and only make 20 grand profit.
Better still have a big turnover with a huge percentage of profit!