Hundley was indeed atrocious with Green Bay, but has looked a lot better in his preseason and limited game action with the Cardinals. Maybe Kingsbury's offense suits him better. I think he's a perfectly adequate backup in AZ.
Interestingly, with only 11 passes and 7 rushing attempts, Hundley had a lousy 58.5 passer rating this season - but a pretty good 76.4 QBR.
Keenum did go 11-3 with a stacked Vikings team and almost had them in the NFC Championship game. Certainly nothing to scoff at! If the Cardinals were a year closer to Super Bowl contention he might be worth the price, but I think he'll expect a much higher salary than Hundley.
... dave