I would say that you final cost is going to be regulated by how good you are at wheeling and dealing and your mechanical abilities. The more you can do yourself, the more money saved. Every time you have to farm out labor the costs go up up up.... How well your shop/garage is equipped is going to dictate you final costs since you may be finding tooling costs may set you back a few bills in addition to the cost of parts. LS1Edit or HPTuners software will set you back around $500 if you don't have it already or you will need to contact someone such as Allen to program your PCM. There are so many variables envolved that are limitless. It all depends on how deep you want to go. You can spend a fortune on speed parts or you can stay bone-stock. I would find it hard to believe that a person could do a conversion for less than $5000. I know I have about that much tied up in mine and I was very thrifty and did all the work but the drive shaft modification and the rebuild of the heads.

Parts needed?

Complete engine and transmission with wiring harness and PCM
Corvette accessories have the best clearance in the alternator area allowing the engine to sit further back in the chassis.
Motor mounts..street and performance or gmcwantsls1 makes them
electric fans
engine wiring harness conversion
drive shaft modification as needed
exhaust...LS1 car will not work. Late model Vortech truck manifolds or pricy headers. Pipes will have to be incorporated into the factory exhaust or a new system installed.
Transmission crossmember may or may not need modified to fit new transmission.