Here are my sources, in case anyone is interested: (The prices I paid, shown above, do not include shipping, which is free in some cases but not in others.)

Z Stepper: https://www.amazon.com/gp/product/B074JJQJVP Y Stepper: https://www.ebay.com/itm/121146152794 (Awesome deal, and they still have some left) X steppers: https://www.amazon.com/gp/product/B00PNEQKC0 1000mm SBR + 4 Bearing Blocks: https://www.ebay.com/itm/183042235383

Some sellers on eBay and Amazon have sales periodically. The SBR I bought from Amazon in 2015 went up from $47 to $110 in that time, but some eBay sellers have it cheaper. This is all, of course, assuming someone wants to build the best machine for the least money.

Also very useful is Blue Demon Triple Play aluminum brazing rod: https://www.amazon.com/dp/B01MCTUIUN This stuff is nice. With some practice, I was able to make some nice strong beads, and even built an aluminum cane for when my back says it's going to rain.