Are you sure that the $521 included all those extras?

I'm uninvolved in this transaction but when I bought my 176C a year ago it
was uncommon to get just the unit below $500. If I remember correctly, I
paid mid six hundreds for the unit("Power Cable and Mounting Bracket" were
included), Bluecharts, a 64MB memory card. I think the USB adapter was going
for $75 or so. I opted out on that one.