I might have to look into this. The original thought for all this was that I wanted outboard bearing cranks because they would be simpler to disassemble for our travel tandem. Helicoil is not an option there because of the spindle, obviously.

But now that I see the prices on the above options, helicoiling square taper or octalink cranks is definitely an option. Davinci still leading the field for the non-outboard bearing cranks though.