99 Tahoe engine rebuild

Well I just dumped 2k on the rebuild of my tranny and when I drove it back from the shop it started making a clunking sound. A mechanic friend discovered that there was almost no oil in the truck so we added 4 qts. I check this 4 wks ago and I added a qrt, where it went I have no idea. Well needless to say it was still making the clanking sound towards the bottom of the engine and my friend said that my engine was shot. He said that I would either be able to rebuild it or buy a new one.
He can't do it for me so I was looking for a ballpark figure that I would be looking at spending as well as any tips or suggestions. Also, I have 140k miles on the tahoe and it's the 5.7 Vortec.
I'm somewhat lost, because I don't know if I should take it somewhere for a rebuild or just suck it up and buy a new engine.

Thanks guys.
cp