It'd depend on the location, the type of broken pixel (stuck or dead), and what the store and/or manufacturer's dead pixel policy is. I used a monitor for at least a year that had 3 solid lines of dead pixels on. They split the monitor into 4 equally sized horizontal bars. That's a total of over 3000 dead pixels, and it honestly didn't bother me. I also didn't pay for that monitor, so I might have cared if I had.
I buy cheap monitors, I don't expect perfection in a $100 17". But so far I've never had a dead pixel on any monitor I've purchased (I think I own 11 LCDs now?). I had one turn pink and get very washed out (a 4 year old Dell refurb) and the one with the lines, but so far I've had great luck with LCDs.