My 3D printer consumes three things: my time, electricity, and miles (*) of plastic filament.
To date, I've been going through plastic at about two kilograms per month. At about $60/kg (including shipping) for the manufacturer's plastic, that's about equivalent to a bad Starbuck's habit--an affordable luxury, especially since I don't otherwise have a Starbuck's habit.
There are two problems with buying plastic from the manufacturer, though: first, it costs $60/kg and I'm cheap. Second, it only comes in white.
So I have been on a hunt for alternative sources of 1.75mm ABS filament to feed my 3D habit. Hobbyist 3D printers seem to have settled on 1.75mm ABS and PLA as the "standard," so there are may sources including other 3D printer manufacturers, third party vendors, and guys who bought a palletload of plastic filament and sell it on eBay.
So far I've tried five different sources of filament and I'm still evaluating two others. I've paid prices ranging from $25/kg (for bulk orders) to $60/kg. And I've discovered that all plastic is not created equal.
Size: To get the best and most consistest results in my printer, the actual diameter of the 1.75mm plastic filament needs to be between 1.70mm and 1.80mm. Plastic as small as 1.60mm and as large as 1.80mm can be made to work with some effort, but diameters outside that range will not feed properly.
So far this has been the largest challenge in finding reliable suppliers. I've bought reels of filament which vary between 1.55mm and 1.95mm over a distance of less than two meters. That's simply not going to work. The result is jammed filament, failed prints, wasted plastic, and frustration.
Of the five suppliers, three have delivered plastic which is consistently in-spec: Up (the manufacturer of my printer), Makerbot (which makes a competing hobby printer), and ProtoParadigm. The guys at ProtoParadigm get extra credit for offering bulk 30-lb spools at a substantial discount, but you have to special-order it and wait a couple months for delivery.
Plastic: It turns out that there are lots of different kinds of ABS plastic. The stuff Up sells is an extra-strong grade which gets extruded at 260C. Most other suppliers offer a lower grade of plastic which they recommend extruding at between 200C and 225C.
So far, every ABS plastic I've tried has extruded just fine in my printer, though with the lower grades of plastic it is often harder to remove support material and there tends to be more warping and lifting from the print surface. If I was trying to get perfect models every time this would bother me, but I consider this a worthwhile tradeoff for having a choice of colors and lower cost.
Colors: If Up offered a choice of colors I probably never would have started looking for other sources of plastic. Right now I have reels of about ten different colors, including glow-in-the-dark and metallic silver (which is more like graphite, but still looks sharp). Printing in color gives much more appealing results than boring old white.
Quantity: Most retail sources sell ABS filament in 1 lb or 1 kg reels, at prices around $45 - $55/kg including shipping. Special colors, like fluorescent, glow, and metallic, often cost a few bucks more. A few carry 5lb reels at a discount. ProtoParadigm lets you special order 30lb reels for a significant discount.
I'm just starting to explore ordering directly from wholesalers. Minimum orders range from 10lb to 25kg, making this a little risky since I don't want to buy a year's supply of plastic and discover it consistently jams my printer. On the other hand, wholesale prices seem to be generally around $20 - $25/kg including shipping, so there's the opportunity to save a lot of money if I can find a reliable source. Wholesale orders also seem to have one to three month lead times.
Stock: Right after Christmas, most sellers of 3D printer filament seemed to go out of stock on most colors. I'm not sure if this is a post-Christmas spike in demand or what, but at the moment it is a challenge to find many colors. I'm hoping that availability will improve over the next month or two as the wholesalers catch up.
My Buyer's Guide for Plastic to Feed an Up
Up: You can't go wrong with the manufacturer's own plastic. Pros: best performance and strength. Cons: comes in white only; more expensive than other retail sources; ships from China so options are limited for quick delivery.
ProtoParadigm: These guys are obsessive about quality, and their plastic works really well. Pros: Competitive prices, bulk pricing for 30-lb reels (by special order), very responsive and easy to deal with. Cons: Limited colors, but they say more are coming soon. Right now they have Natural, Black, Glow, and Fluorescent Green, all in stock.
Makerbot: A little more expensive, but consistently good quality. Pros: Lots of color choices, quick shipping, and easy to deal with. Cons: Right now most colors are sold out; prices are at the high end.
3dPrinterStuff: I can't recommend because the plastic they sold me was consistently inconsistent in the filament diameter. When I complained about the poor quality control they were not responsive. They used to have a good selection of colors and some 5-lb reels, but all they list now is black and white.
3dInk: Also can't recommend because of out-of-spec filament diameters, but the owner was helpful and offered a refund when I complained (I refused the refund and am using the plastic). There's hope here. Very competitive prices and respectable selection of colors, though all but one are sold out right now.
(*) My rough estimate is that so far I have used about one mile of filament in my printer. Give or take about a half-mile.