Here the load down. My phone, an iPhone 4S - although any phone with decent app will do the trick.
The GPS app I use?
MotionX GPS ($3.99) plus voice command subscription ($24 for the year).
Keep my iPhone in my pocket for the most time, but when needed I pull it out and mount in on my Just Mobile Xstand Go (ST-169A) ($40). I can see an listen to my navigation directions.
How?
The phone is connected to my audio system wirelessly via the AUX port (I do have the iPhone connector for my Spyder but do not use).
Wirelessly?
Yes, using a Bluetooth A2DP Adapter - Miccus BluBridge mini Jack RX ($40.00). The phone is paired with this device. The beauty is I have full iPod music streaming wireless HiFi to the aux port. I get to stream even Pandora or any Internet Radio including XM, if I had a subscription. When direction are needed, MotionX actually fades to blend the music with the directions/instructions (ducking the music sound).
The only drawback to this setup is waterproofing the iPhone. Which can be done with a leafproof case. I personally chose to buy a Mophie case which is actually a battery extender which works nicely on longer trips. The iPhone with the mophie battery case runs for over 16hrs. Continues music playing, some browsing, navigation and occasional email checks. You can always charge the phone with the rear port while still enjoying music, gps directions and shielding from the rain if necessary.
Overall, this solution has been much more cost effective for me without having to do many mods to mount and wire external GPS. Oh, btw. MotionX gps offers real time traffic, up-to-date maps and even 3D maps.