My Toyota Tacoma TRD is a 3.4L V6. It has an intake and exhaust which gives it a little fuel economy. It is roughly $90 to fill it up at $1.30/L (where our gas is now) With that I get around 350 miles (my truck is from the states) on a good day to a tank. Which is 560 km. It is awful with any kind of weight in it, or with a trailer. But its better than my 5.7 2500.
As mentioned previously, I think something along the lines of a Toyota Hilux (must be imported) would be an excellent idea. They get about 35mpg with the 3L diesel motor, due to my understanding. They can be quad, single or extended cab. When you import them they all have around 100k km's on them, nearly all of them are in mint shape.
Say what you want about imported vehicles, but these Hilux's are nearly indestructable. They will far outlast any domestic diesel, or gas truck. Mini or full size. They require the same maintenance, but you can beat the crap out of them. They're around 10-15k and this is for a mid to late 90's truck. That is the bad part...