if you are not in a hurry, there are various freight forwarding companies that will ship LCL (less than container load). Some of them will store your stuff until they have a full container and ship it that way.
ones such as this
www.shipping2australia.com/shipping-from-usa-to-australia.htmmight be an option. If you can say it is personal effects that are second hand you will probably save on duty etc. But if you sign a stat dec saying it is less than AUD1000 then you shouldn't get GST.
but there are others that specialise in motorbikes etc. that also ship other stuff LCL.
Just ensure you get the costs of clearance in australia in included in the price. I would say door to door, but it is probably best to pick up your SUP from the depot when they unstuff the container. Just make sure the quote is all in.
Clint