We don't need Pierce. Like Tiger_Dirt said, the guy has way too many injuries. He's a walking infirmary. He's a tough SOB, but we are good at QB with Glenn, Porter and Trafralis (don't forget about him).
If its to be second string fine. Its an upgrade over Porter. I just don’t see Porter ever being a decent starter and if Glenn goes down for myself I don’t have to confidence in the guy to win on a consitent basis. Pierce can do that and likely flourish as a back-up for 2 or 3 game stints if Glenn goes down. If he comes for cheap do it no questions asked.
I wouldn't want to grab him. Porter is an excellent backup QB and if he got traded, he has the potential to be another Anthony Calvillo which is the last thing we want to give any team, ESPCIALLY the Arblows.
I wouldn't make a move for another QB at this point unless one of our guys is planning on leaving. He might just be an extra guy brought into training camp.