That project is a little different considering they put in an Ecotech which is quite a bit more money than the LS4. They also put in a 4L60E and new transfer case, I will be retaining the stock 4L30E and Borg Warner transfer case.
A slightly used LS4 runs anywhere between $800-$3,000. It's the labour and wiring harness that will be the most costly but my mechanic has told me that it won't run me $8,000 like it would for a new- stock motor