Savage42 I just put a Ls1 in my car. It took me 4 weeks to do the swap, this is spending a few hours a day after work. It can cost you 10-15,000 if you do not do the work. I do not have a shop, just a garage. 
  
This is my cost 
  
Ls1/4l60e   $2500 
Drive shaft $200 
Radiator     $200 
Fuel system $400 
Header        $700   you can use stock manifolds--they will fit 
Exhaust       $200 do it yourselfe or 300-600 at a shop 
Mounts        $free just make them 
Air intake    $200 
  
  
It cost me about $4900 for the swap and it could of been less if I used the stock headers. The Ls1 swap is a very easy swap, it takes about the same time that a LT1 swap takes.