The main issue is that your numbers presuppose $1000/person for 50M people. I think that there is undoubtedly enough sick people to treat, but not solely in America.
The first problem is that the majority of the world is either poor, and cannot afford $1000, or is part of a socialized single payer system where Anavex would have zero leverage -- the government or EU or whoever will tell Anavex we will pay you $100/person and take it or leave it.
The second issue is that you do not really factor in all the costs associated with scaling up to serve a population of 50M. It will be a lot more substantial than you think.
The third issue is that 50M shares means only another 9M or so issued; even at $8/share, that will barely be enough to get through the P3 trials and regulatory process. Anavex will inevitably have to partner with someone who can front the costs of manufacturing and marketing the drug, and this means that the 50M share count by which you divided the revenues is moot.
Finally, there's the issue regarding patents and expiration and generics and other drugs that will be developed that will erode market share. Does Anavex have patents for every country and how long will those patents last before they expire? You're looking at a relatively short period of time for Anavex to try to grab as much cash as possible.
I think the best comp is Aricept, which had peak sales of around $2.6B and in the last few years that number has fallen steadily with the introduction of generics. Why would Anavex's drug be so much more lucrative than any other previous standard of care, even with an uptick in the number of people using it?
I think a safe bet is to say that if Anavex works, you can forecast potential revenues of around $25-$30B over an eight year period. So let's round up and say it's $4B/year revenue, and we'll even say that is pure profit so we don't factor in tax or any other expenditures. I also think it's safe to assume that when all is said and done, we'll be fully maxed out of OS. So the very peak would be around $400/share, which is possible -- REGN and others have hit that mark. But more likely, some company will make an offer for $5-$10B at the end of a successful P3, and Dr. Missling will accept it. He has 1M+ shares -- it's hard to turn down $100M.
