If you Google you'll find links of varying quality. Direct statements from Sony, but Nintendo and Microsoft not so much. It's all third party analysis which I find compelling.

Does your analysis still hold if the Steam Box base model sells for $600? Analysts estimated the BOM at $425 - $450. Add a little bit for RAM inflation, and Valve can still sell for $600 and technically be selling without subsidies as promised. They also promised to price it "like a PC". Lots of PC's sell for $300, so that also doesn't really constrain them.

I don't think your analysis depends on the Steam Box selling for higher than $600, but you're a better judge of that than I am.