2004 Oldsmobile Alero Lower Ball Joints?

I recently purchased 4 new tires and I noticed that the front passenger side tire had alot more wear than the other tires especially on the outer edge of the tire. The tire store told me that they could not do the alignment because the lower ball joint on that same front passenger side needed replaced. The car doesn't make any wierd noises, the steering does not have a lot of play. Should I get it replaced and how much would that usually cost? Is there a way to check to make sure?

Thanks,
BaronB