That's my reaction too: how did Fister get so cheap? It seems that groundball pitchers have lost value, now that Cherington can no longer overbid for them.
"Here’s the fact of the matter: as a starting pitcher, between 2014 – 2015, Fister lost 1.9 miles per hour off his fastball. He’d already lost about a mile from the year before, and he’d already lost
another mile from his career peak. But, we can focus mostly on the most recent drop, because Fister was effective two years back. An easy explanation is that, last year, Fister struggled with forearm discomfort, that sent him to the disabled list. Injuries generally help explain these velocity drops, but what’s curious is that Fister didn’t actually regain any strength upon his return. Previous to hitting the DL, Fister’s fastball averaged 86. After coming off the DL, as a starter, Fister’s fastball averaged 86. It played up a tiny bit when he moved to relief, but that’s what almost always happens. The fastball left him, and at least last year, it didn’t come back."
http://www.fangraphs.com/blogs/astros-take-the-doug-fister-chance/