At the end of the day you have to consider your time. If the hours you invest in the 5.3 are justified, then have at it.
A better deal is buying a salvaged car and parting it out, get the engine for free!
Better yet, build a company selling car parts, and never have the time to finish your car........
Wait
No
That's the gin talking.
I think Matt's point is the oft quoted price of truck motor pullouts neglects to mention some of the necessary incidentals.