MAKE YOUR OWN MUSTARD!... seriously
It is easy and economical. Here is a favorite recipe of mine:
http://marikosakata.com/raw-vegan-homemade-mustard/
Mustard seeds are a great source of selenium, omega-3 fatty acids, and manganese. They also supply phosphorus, magnesium, copper, and vitamin B1. Use them for pickling, to add flavor to stews and sauces, or to make your own mustard!