I'm new to this forum and new to my 370Z, but I also found myself in need of a nav unit; I intentionally avoided factory nav as I find it over priced and dated technology. I don't know if you have a smart phone, but if you do you might consider an Pioneer unit with advanced app functions.
What I got was the Appradio 2. It DOESN'T have nav in the HU, but it does use your smart phone's nav, which I myself like better than any native HU nav. It also has a number of music apps and other useful apps such as dashcommand (
http://www.pioneerelectronics.com/PUSA/Car/AppRadio). For $200 (clearance at BestBuy), I have an always up to date nav unit (I use Waze for the iPhone - nice because radar detector use is not allowed in VA), an Internet browser, engine diagnostics, youtube, weather, Bluetooth, and a backup camera (bought separately) all,displayed on a 7" touch screen.
It doesn't work on all smart phones (select Androids iPhones), but for someone like me it saved me a heap of money and I like what it does better than comparable traditional HUs.