I thought that might just be Amazon resellers capitalizing on marks being too lazy to go off site at first when they were $280 at Microcenter (still crazy expensive). [0] Then Adafruit had them for the same $350! [1] And it really does seem to be driven by the ram too the 4 GB model is only $130 (or $104 at MC).
Just like eBay, an Amazon listing for a certain price does not mean the item is actually /selling/ for that price -- especially with badly-coded dynamic re-pricing algorithms hooked into listings these days.
It's not completely out of line with other RPi sources listed on the RPi Foundation's own site. It's the same price as Adafruit for example but about $50 more than Mirco Center (though that is for instore pickup only so only for people lucky enough to live close to one).
[0] https://www.microcenter.com/product/702590/raspberry-pi-5?rd...
[1] https://www.adafruit.com/product/6125?src=raspberrypi