Impact rated tinted safety glasses: $ Very reasonable
Short length of 90kg kite cord: $ Bugger all
A couple of drops of rainex: $ Not much
Having a pair of glasses that you don't worry about and never come off: Priceless!
A couple of notes:
- Using a 'rolling hitch' is important! It slides to tighten and wont slide back under tension
- Elastic headbands are just that, elastic. In a crash they can stretch and allow the glasses to slip off into the briney (feel free to ask me how I know this)
- The loop at the end of the cord can be clipped to a small carabiner tied to the zip strap on a wetsuit (I do this but the glasses have not come off yet)