With a price difference of around 15p per litre or 30% cheaper kerosene is a much better buy. Any greater than 10% cheaper would make kero the better buy
The McArthur article I linked above suggests that you need 5% more kero than gas oil for the same heat output, so that would be the break even point. Last harvest, kero was at a massive discount to diesel, probably helped by lack of demand for aviation fuel. My drier runs on kero but wouldn't be hard to swap to diesel.