Not sure why you need the 890 pro in your case. The pro is multi-zone capable for controlling up to 6 different rooms and having up to 6 extenders. I think you'd be throwing money away since your system isn't multi-zone (per your other thread). Besides, the pro doesn't even include the extender, unless you found a seller bundling it.
890's are only $244 on amazon at the moment. They're new and include the extender as far as I can tell. You could save another $100 if you got something like a 670 and a next generation RF system. And you could save another $60 if you go for a refurb (they're $40 at tigerdirect), which have all been mint in my experience. The only thing you'd be missing with next gen is addressable blasters.