Try this... you can get it for less than $300 and install it yourself. (EDIT: looks more like $320 with the antenna added.)
http://www.mynissanparts.com/pc-314-...ite-radio.aspx
For some reason, they list it under the Armanda, but not the Titan. You'll need to verify it's the same kit, but I'm 99% sure it is. Contact the dealership that runs the site and ask them if it's the same kit. If it's not, then I'm sure that they can sell you the right one.
Here's one listed for sale on ebay for $388 with everything included...
http://cgi.ebay.com/ebaymotors/Nissa...spagenameZWD1V
I installed an XM Commander on my last vehicle, and installing an OEM kit should be about the same level of difficulty. I researched to find the right wiring locations, and then spent about 1.5-2 hours installing it.