I feel kind of silly for not being able to see what's wrong with this, but it's starting to drive me mad.

So could someone tell me where I'm going wrong?

PHP Code:
  else if(submit_form.price.value == "" || isNaN(submit_form.price.value)=="true"){
  
alert"Please enter a price." );
    
submit_form.price.focus();
    return 
false;
  } 
Thanks very much,