I am sure it is by weight. Typically, plastic spools go for around $18-35/kg. Every company seems to shy away from guaranteeing length. But, if you know the volume of the part you want to build, it is almost a 1:1 transfer of material.
Lulzbot says, "The LulzBot AO-101 is one of the few desktop 3D printers on the market that can print with ABS and PLA plastics. With some simple adjustments, you can print with a wide array of experimental materials like wood filament, nylon, polycarbonate, polystyrene, and glow-in-the-dark materials. "
I am sure they will have to verify the type of materials first. So, I don't think this will be printing stainless steel from spools any time soon.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.