Let's review a little.....

Uh, he wasn't asking you if you had a new engine, he was saying you need a new engine. Rod knock comes from a bad rod bearing. Even if it's a different bearing, it isn't going to get better. So....
Either replace or rebuild, but if you want to avoid the raping part, I'd probably just go for a quality used motor. Heck, if you have some mechanical skill, you could do it yourself.