A complete overhaul of what you have would probably run close to that price anyway. But I'm speaking from MA where everything is mega-expensive.
The best thing for you to do is shop around your area -- stop in a few tranny shops an ask what an overhaul would cost, and ask what it would cost if you got a used tranny to swap out. Hit a few local small garages too and ask the same questions. I'd hit the local salvage yards too & see what they have. They have the book (can't think of the name right now) that shows what fits what from any year, make & model - so they'll know what years Titan that tranny will fit & work in. There won't be too many of them since they're not that old ... but every so often someone will total one & it'll end up there getting picked for parts. More often in cities. Could even look on eBay for one that's being parted.
Here's one, but not for parts - they're selling the whole truck. Great deal though considering the mileage & year: http://cgi.ebay.com/ebaymotors/Nissan-T ... 2eb9c2b66d
You might get lucky & find someone that knows these trucks, and knows what the tranny needs for a permanent fix. In that case, fix it & keep it. In MA it's "cheaper to keep her" as they say, due to the $75 title fee, sales tax, etc. on another vehicle.