I have a quiver kaddy, use it all the time to walk the 800m to the local, lock it up with a bike lock. Also use it a bit to take the Kids boards, towels, mask and snorkles, boogie boards, frisbees, cricket sets, lunch esky...... etc etc to the beach..

Good bit of kit I picked mine up from a surf shop for way less than $500. I can also tow behind bike and it will get a bit of use taking the nippers boards down to surfclub in the commig weeks.
You can build a similar thing to the mule from a bunnings $30 trolley... thats what I would do next.