If you want a kenwood unit but can't afford it right now, consider purchasing the DDX812 double din unit, then getting the KNA-G510 navigation module to go with it sometime down the road. That way you get the performance you know you want, without dropping all the cash at once. The best part about doing things this way is that you can upgrade receivers and keep using the same navigation module.
This is a good idea and I actually have a DDX812 + KNA-G510 myself, but the final thought of upgrading the receiver and keeping the nav has some disadvantages now that the DNX9140 is out...
Speaking of "unauthorised" prices (e.g.
eBay, online, etc.), you will save about $100 over the price of the same unathorised DNX8120, going with the separate DDX812 and KNA-G510 units, so that's a plus. (I actually saved about $200 because I got my DDX used in like-new cond'n for a very good price.)
Note that no matter if you get the DDX authorised or unauthorised, if you add the KNA-G510 to a DDX unit you will have to buy it unauthorised otherwise it is big money and that will just be pointless.
Another positive I thought of is if you have the G510 installed somewhere away from the HU, and someone steals your HU, at least you still have the nav so it's less money to replace.
The little hitch about upgrading the HU and keeping the nav happens now because the DNX9140 has an all new nav interface, much like the newer Nuvis have. That's why it's a DNX
9140 not DNX8140. Using a DDX814 (there is no DDX914) plus the KNA-G510 will therefore not net you the same thing as a DNX9140. Instead it will net you something similar but with a lesser nav package. Unfortunately I don't think Garmin or Kenwood is updating the G510 (or older Kenwood DNXs) to have the newer interface (it probably isn't even possible). In the end, though it sounds good in theory, there's little to be gained in upgrading a DDX812 to a DDX814.
Of course the DNX9140 is not cheap right now anyway, so if the newer features it has aren't necessary it's nothing to bother about.