Strictly speaking, it is not a Trappist beer (there are only 14-15 of these all around the world) but an Abbey beer (there are hundreds of those in Belgium and many more in other countries).
I assume they are as expensive in the Netherlands (you live there, aren't you?) as in France. This is why I fill the car with (full) bottles of beer when I drive to Belgium once in a while.
I am still in China. So I cannot drive a car to Belgium :3
I will be back in NL around the summer ^^
Ah yeah... definitely too far to get a decent Belgian beer at a decent price ;)