I happen to have that particular combination, although I received the mouse as a gift after purchasing the Cordless Freedom Optical (now discontinued). The newer ones apparently have a slightly different button configuration; I'm referring to the programmable buttons found on the upper- left and right sides of the keyboard.

My point is, regardless of cost, I will never go back. I've only replaced the keyboard's baterries once in over 2 years, and the mouse is rechargeable. And with the extra programmable buttons and excellent range (with fresh batteries), I say it's definitely worth it.