How much money can I expect to get if I submit snowboard designs to
companies? What's the best way to go about freelancing as a snowboard
designer?

If you simply submitted a design out of nowhere, they would most
likely steal the design or ignore it.  You may not want to believe it
but I have been in the industry for a long time.  You must be an
"insider" or have an "in" to get any $$ from these companies.