If you're assuming $1.825B in peak annual revenue, applying a 4.5x multiple (reasonable for CNS assets) results in a $8.2B valuation, or about $81/share, assuming 100M fully diluted shares.
Falconeer66's numbers were, as he stated, very conservative. Historical data exists to show us that a valuation of a BP for a Phase III AD drug is in the $20 billion range. In AVXL's case, let's assume regulatory approval by FDA and EMA but also recognize that a marketing/distribution partner is involved so let's be conservative and cut that valuation to $10 billion, or about $100 per share using your fully diluted share count. Following regulatory approval, that AVXL valuation would likely double.