For straight foils, you can get by with CNC cut foam cores (high density foam) and laminating carbon over them (lots of carbon). If people are interesting, I can cut 100 PSI foam on my CNC for reasonable prices.

The issue is when you go longer or curved; in these cases you need a CNC router machined core and a PVC based foam or wood core. Finding someone that will machine cores or molds for reasonable prices is not a trivial task, I have a few sources and may evaluate designing and building some curved A-Cat foils if the business case is justifiable.

As far as aluminum is concerned, built properly you can approach composites in weight and strength, but time wise it would take longer than the methods proposed above (unless you are THE metal guy). The corrosion issues posted above have never really been solved, take a look at any aluminum vessels (boats or seaplanes come to mind) after 10 years. Foils would not hold up very well to this abuse!