I don't think it will be much cheaper than $200. plus.. it's not the speakers that are optical. The logitech gives you a pod that would process the optical output from the projector. You could do the same with some normal home theater speakers and a cheap reciever w/ optical inputs. You might be able to find a cheap htib if you wanted to go that route.
Man, this thread is confusing. Optical speakers? A projector optical output? LOL. Anyway, If you can go with less power the Logitech Z-5450s can be had for under $250 shipped.