Even 'addicts' are rational consumers, they just have a warped set of values. As in, if I get burned by Frank the Dealer, I'm going to look for a new place to buy smack because I must have it, and throwing money at Frank isn't accomplishing that goal.

That could be true, if for no other reason than the fact that the material will be proprietary. My lab uses an Objet Connex 500 (with a voxel size of .04mmx.04x.02), but 3.5 kg of basically any material runs over $1000. This is in no small part because we must buy cartridges directly from the distributor (think of somebody with one of those "free" Dell printers with $50 ink, except there's no other competition).

You can't beat Lego Technics in terms of structural toys. They have, in my opinion, the very best 'complexity of what I can build/how hard they are to use' ratio there is, which seems like exactly what your kids want. My roommate just used them for his final project in a grad-level dynamics course to build one of these (not full-size, of course): http://www.youtube.com/watch?v=par9zbTSN58

Not to mention the fact that the drugs would be much more trustworthy; nobody would risk cutting their product with something harmful if there were a legal paper trail back to their business. The other danger of cutting, even with a harmless substance, is that it's impossible to know the true concentration of the drug when you buy it. This is exceptionally significant when talking about drugs with low dose and high potency, like LSD. If the system were regulated with laws allowing the consumer to inquire exactly what's in the substances they buy, the system would be worlds safer.