I've never used balsa as a core material, however I'm very familiar with balsa from other hobbies.  I'm thinking it may be my best bet as a core that needs to be shaped. I know I'll have to drill it.  What else do I need to know that is different from a cloth or honeycomb based core?

Thanks for the advise.  So the thin sheets from the hobby shop that are normally used on RC airplanes wont work?  The shape I'm making is pretty flat.  Just has a thin airfoil shape.  I was also looking at foam, but figured balsa would be stronger, even though the part won't receive much stress.