The DX7 radio system retails for $349 from Horizon Hobby. They are the distributor. You can also find it for less at other locations, as pointed out above. The only problem is if they have them in stock. It's a pretty popular radio system.

There was a thread started a couple of weeks ago with someone asking the same question with one response showing a system available at a different hobby supplier at just under $300. You might peruse through the previous threads and see if you can find it. I checked that one and, at that time, they were in stock.

As far as the DX9 is concerned, well, I'm not sure if Horizon knows when they will be in stock. I know that the receivers are around, my LHS has at least one in stock.