...the folks over at Tromix can whip you up a .458 SOCOM AR knockoff with an integral suppressor. Oh, that's just ridiculous. Way overkill. Nobody would ever...uh...
How much are they going for?
No idea. Their baseline models are all right aournd a Grand. For a special toy like this one probably an extra thousand or two. Send 'em an e-mail and ask. Assuming you can get all the BATFag forms in order, they hsould be able to whip you up one.
I'm still planning on their .50 AE upper for a future project. Next upgrade for the Mistress is converting her over to an M-4gery "Space Gun".