Dave's right. I had this happen to me once. Blew out a ball joint and they wanted $100 for the joint plus almost $150 in labor. They also wanted me to buy a used tire (the old one blew out after I drove with the control arm rubbing on the rim to the garage.
Long story short, they replaced it after I specifically said that I wanted an estimate first. At least then I could have gotten a ball joint for less than $100! Anyway, I threatened with legal action when they called a week later telling me it was done. I drove away and only paid the shop's cost for the joint.
I never go there again.
However, if you said "just fix it" you're pretty much stuck unless they gave you an estimate before working on it and they went over that.