For those of you scrambling to find a source for inexpensive filament, we found one: Seacans. They have a reasonable selection of colors that should satisfy most buyers, but the important thing is price. You can buy a 1kg spool of 1.75mm filament in either PLA or ABS plastic for only CA$19.99. That's USD$8.08 per pound for you non-metric folks.
This is one of the least expensive sources of filament we've found, but there are some caveats. We don't know the reliability of this vendor. We don't know the quality and consistency of their products. We also don't have any certification of non-toxicity from them, as filaments from some overseas sources have been known to use lead as a colorant. Shipping costs will be added, and they may vary considerably depending on where you're shipping to.
Nevertheless, the price is low enough to warrant an experimental purchase.