I think the estimates are that $400 is reasonable for the hardware. It's not particularly great, and makes some sacrifices for cost saving, which is fine. Like 8GB VRAM is pretty low for modern hardware. It's enough for a lot of games, but modern AAA games it's probably a little low.

I agree, $300 will be good enough people will get it for a computer. That's what selling at a cost does. These manufacturers already get a bulk discount that buying as a consumer doesn't, and selling it at cost makes it even lower. It'll definitely be a good value for low performance computing, and I'd wager that's part of the goal too. It isn't just a console. It's also an alternative to your computer and, importantly for Valve, gets you out of the MS ecosystem.