I went down this path a few weeks ago. It seems that no matter where you go, the rebuild cost is just about equal to the replacement cost, regardless of who you ask. So, it'll cost you $950-$1000 to rebuild, or $950-above for replacement (w/o core charge).
I'd recommend checking:
cumminsstuff.com
se-power.com
realdiesel.com
piersdiesel.com
Craig