As MK14 showed, they are available on the pi hut (and a lot of other places) on a regular basis, at least the pi 4 (not sure baout the pi 400). Sure stock varies a lot these days, and the 8GB version seems to be the one hardest to get ahold of. But 4GB versions are relatively easily available. Anyone willing to pay more than the official price, at this point, would be an idiot. Unless they are in a big hurry and it happens not to be in stock just the day they want to order it.