About the Yarn
As the pattern recommended, I used Plymouth Encore (75% acrylic, 25% wool). Unlike the pattern's recommendation, I used a purple color (often described as "English Purple" although Plymouth doesn't officially name their colors). The balls I bought were on clearance, as the color has been discontinued; a quick search of Google shows that one can expect to pay between $4.50-$5.50 a ball if one buys online. I would expect that buying from an LYS would cost about $6.00 a ball.
How much yarn?
I had some trouble deciding how much yarn I'd need, since I wasn't following the pattern exactly. I bought 25 balls and worried to no end that I hadn't bought enough. As it turned out, I had two full balls plus a couple of scraggily ends left when I was done. For those making the pattern exactly (one afghan of 20 squares, plus two pillows of two squares each, all three items with borders), be aware that although the pattern calls for 20 balls of yarn, buried deep in the back in the finishing section they mention that you might need an extra ball to finish the pillows. So I would recommend buying 21 balls of yarn rather than 20, if possible.
For those of you who might be tweaking the pattern like I did, and wondering how much yarn you'll need, here are some observations I made. Your mileage may vary.
Each square: 1/2-2/3 ball, depending on size and complexity.
Afghan Border: one full ball knit me about 37 or 38 twists (about 6 feet 2-4 inches) plus one corner.
Seams: Used the dregs of yarn from the partially-used balls. Probably less than a quarter ball for all the seams.
Pillow Border: No idea. Sorry.
Here's some info about the yarn itself, taken off the label:
Knitting Worsted Weight
75% Acrylic 25% Wool
100 g (3-1/2 oz). 200 yards.
(Knitting) Metric 5 - 5-1/2 or US 8 - 9
(Crochet) Metric 5 or US H/8
Machine Wash and Dry 80 deg F
No bleach. Dry clean, any solvent. Iron, low heat.
Made in Turkey