Isn't the MP5 blow-back, stamped metal, and cheap to produce? Admittedly it's delayed blow-back, but there's still noting in it's manufacture that's all that inherently expensive. Stampings are cheap. Hammer forged barrels are cheap. Plastic moldings are cheap.Heck, they make them under license in places like Mexico, Pakistan, and Turkey. It's not like they're all hand forged by übermenschen under the direct supervision of Thor himself.
I've never heard from anybody who actually used a variety of subguns who thought that the MP5 was the pinnacle of Teutonic perfection that the fanboys seem to believe as an article of faith.