I guess you could get a crap tonne of two liter bottles
Fair play to you shroomy, that is a grand idea.
I had been planning on doing my next one in a couple of two liter bottles grafted together to make a nice deep tube but I have to say other than the having to drop a little coin, I really like the idea of the pvc.
I'd say avoid the PVC, if not for leaching chemicals, then for the general BAD karma involved in the production and disposal. No telling what happens to the other stuff in the pipe once it's been under enough UV and starts to turn that brown color - unless you paint it with UV resist paint.... but then there's more chems...
I guess you could get a crap tonne of two liter bottles into the space
2 to 2.5 liters will get you a solid quarter ounce, if you do it up right.