BS options val, page-2

Volatility should be 100% (change of 100% over 12 months)

I would set the interest rate at around 8% - some set at 10% as a rule of thumb (Buffet) - but with such low rates across the board perhaps drop back a bit

Don't set the interest rate risk free rate of return at 2-3% - you have to be realistic with the risks involved - you could get 6-8% with high quality corporate bonds or stocks.

Each to their own I guess

Either way oppies are cheap