HI Moon,
as with all mods it will cost but as with all cars the Question always has one answer
why not.
its actually easier from what i can see to convert a wagon.also a canopy is no where near as cool as a windowless van hahaha
But yes it can be done and if you are handy with a mig welder and have access to the needed parts then you might be able to do it with out spending too much,
Its harder to weld in new subframes and put suicide hinges in ,than it is to change whole roof.but unless you have a van roof with windowless sides then its probably not worth it.
cheers Nick