Although you cannot type non-numeric values into price field, you can paste text in and submit. Upon submission page returns to "Start a new auction" screen with message "Error posting auction: bad_cost".
I agree its not a "bug", and perhaps I am being picky being a developer myself, but I know from previous experience that users will do some crazy things. I would have said though that some jQuery could be added to stop the page submission based on the value in the text box e.g.
$('#sellform').submit(function () {
var elCost = $("input[id$=cost-input]").val();
if (isNaN(elCost)) {
alert('Not a number crazy fool!');
return false;
} else {
alert('You may pass...');
return true;
}
});
This is obviously a nice to have as you are doing something with the submission to cater for it.