On road diesel is significantly more expensive than premium in Delaware. I have noticed that diesel seems to be cheaper at stations where gasoline is more expensive. There is more price competition in the gas market and the "discount" stations putting the downward pressure on gas prices invariably don't sell diesel. Most other stations don't sell diesel either. Those that do seem to be making up the discount on gas by charging more for diesel. The stations with more expensive gas and cheaper diesel are probably basing retail prices closer to their wholesale cost.
I always expect diesel to be more expensive in winter because if the increased demand for home heating oil. The price premium for diesel always seems to be lower in summer and the price often drops below premium gas.
I haven't found a source for off-road diesel in my area, but I really haven't tried. The BX really doesn't burn enough to make it a priority. I remember my uncle filling out paperwork a truck stop to buy on-road diesel tax free for his Gradall in Arizona. That would be too much of a hassle for a five gallon can at a time.