Having done this myself, I would very much be in favor of laminating the pine into a rudder blank, shaping it properly and then glassing it with epoxy and cloth, then painting it. (I would also suggest that you consider laminating 3/4 AC plywood since the glue lines are very helpful in determining whether you have a fair curve) This should be an inexpensive and very durable way to go and no more maintenance than the aluminum.
I would be concerned that it would difficult to properly shape the aluminum so that you ended up with a symmetrical, fair shape that was not so thin on the edges that it was prone to easily be bent.
One problem with a wooden rudder is that it will tend to float up at speed and so you need to weight the end of the rudder to keep it submerged. The easy way to do this is to screw lead to the bottom of the rudder prior to glassing th blade. (The lead needs to weigh approximately 8-10% of the weight of the rudder blade).
Even aluminum is light enough that it will be pushed up at speed unless you have a hold down of some kind.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies