I paid $391 for my cast receiver 2 years ago, which at the time wasn't even a premium over a good matching Type 56. Granted, the listing was merely titled "Unusual Chinese SKS" so it probably wasn't clear to many observers that it was a cast receiver or that it was of special interest. Casts aren't quite as rare but are in the same category as the stamped receivers, a peculiar experimental variant that didn't pan out.
I do think the stamped receivers are interesting, but I'm not willing to pay 2.5x the current value of an equal condition Type 56. I might go 1.25x, or maybe 1.5x...definitely okay with never getting one too The People's Alternative Type 56 Receiver Manufacturing Story