Depending on what you are doing....
Just go to car-part.com
find you a 4.8, 5.3 or 6.0 from a truck.
Deercreekauto was pretty nice when I bought my last 5.3
they won't usually come with alternator, power steering pump or A/C compressor nor the brackets. some will have the water pump and harness.
most places will even have a PCM that average about $60-100
But from my experience it's best to just replace most of that while the engine is not in anything.
Figure new accessories cost about $500 combined with $400-1,000 for an engine.
then buy a rebuilt transmission which you can get cheap... early 4l60e's had some issues.
then buy a good rearend and brakes you are still well under $5,000.
if you want an actual LS engine from what I've seen LS1s go for $1,000+