Cheap NFL jerseys and merchandise?

I think it just depends what time of the season that you are looking to buy one, and if you care if there is a chance of it being a "Knock Off."
The NFL would tell you to only buy jersey's from their approved stores....but you won't achieve your goal of getting a cheaper jersey.
From what I've seen, buying one via Amazon or E Bay after the Christmas and initial NFL Playoff rushes is a good timeframe if you still want to wear the jersey during the Super Bowl. If you don't care about wearing at the Super Bowl, then waiting for MLB season to kick off and jersey sales shifting in that direction is another good tactic.