Full namebrand smartphones with this hardware capacity sell for $200 or even less.
So, without full smartphone functionality / 4G / what have you, this hardware would cost Nintendo significantly less to make, barring the screen itself, which is just weird.
Even still, AND with the Nintendo markup, I think $250 wouldn't be unreasonable, but I think $300 is too high.
Then again, with the way hardware makers are marking up their hardware DRASTICALLY these days, you may be spot on at $300... Just... who will buy it?