Need help with suspension squeak

Hey everyone, this is my first post. I haven't introduced myself in the "new member" section yet because I dont have a picture of my car ready.

Anyhow, I currently have a 2003 True Blue 5spd GT with about 69k miles on it. Its my 3rd mustang. For the past year or so, I've been noticing a squeak coming from the rear of my car. It seems to squeak with no pattern. Sometimes its only over rough pavement, and other times it seems to have a cyclical repetative squeak like its rotating with the wheels. Its most noticable if i'm driving by a fence, or a building where the sound can resonate and bounce back towards my car.

I've brought it into a ford dealer and they said that its the bushings of the control arms. Something about how ford designed bushings without the ability to insert more grease. Anyhow, he tried to sell me control arms for $2000! I almost laughed at him.

Anyone have suggestions? Or should I just swap out the entire suspension including the control arms? Thanks