before spending $85 on a t-case extension housing, make sure there's not any other more serious problems. do this by spinning the output shafts in different t-case shift positions, operating engine/trans through t-case RWD with no drive shaft, and if possible, in 4wd with truck on 4 jack stands with a 4 wheels in the air.

with the violence of the t-case breaking, it might have more problems.
if so, $400 for a junk yard is about the going rate, or about $800 for a rebuilt.
i got one here.
http://www.transfercases.com/