Advise me: Replacing/Rebuilding 3.0l Engine

[TheGodfather]

YouTube - 2004 BMW X5 Engine Rattle

Based on my limited knowledge and watching youtube videos, I am thinking I have spun a rod bearing. The X is going to BMW tomorrow to get more details although I imagine they will only be giving a best guess without pulling the engine apart.

Obviously the damage has been done, and so I am probably looking to replace or rebuild the engine.

Anyone here have experiences with this?
What are the do's and dont's of purchasing a used engine.

I have found a used 2002 330ci 3liter engine for $2000 with 84000 miles. Is this too steep for an engine with high miles? My engine has about 100 000 miles on it.

I have also heard its better to replace than to rebuild as far as cost effectiveness.

Also is this something that needs to be done by BMW? Or is this something that can be carried out by a good independent?