I've had a hand in some front suspension work on Contours and in order to replace the control arms the struts need to be removed (which also includes removing the brake calipers and steering tire rod), which is about a half hour of work per side IF all the hardware comes out easy, which it never does, so that would justify giving an estimate with 1 hour for access on each side. Then about half hour for removal and half hour for replacement of the control arm, and another half hour for instalation of the strut and related components. So it comes to about 2.5 hours per side or 5 hours total. Thats how long I figure it would take me, a place like Midas who specializes in suspension work would likely get it done quicker.
Depending on the labor rate I'd say that $500 is a fair estimate. However, large chain companies, like Midas, have lots of overhead, and therefore need to have higher labor rates to turn a profit. A privately owned service center would likely have less overhead, therefore, lower rates and subsequently lower labor cost. But, Midas will offer some sort of written warranty for their work, where you are less likely to find that at a privately owned shop, unless you know the owners well.
Another thing that most shops will do is tack on an extra fee if you supply your own parts. Since they have access to parts at a lower price than you can get at local parts outlets, but charge you the same price so they make money selling you the parts. Usually this charge is equal to the ammount of money they would have made if they sold you the parts.