Hey guys,
First of all, big thanks for introduce new feature such as stock market. It really helps diversfied posssibilites of making money in game.
In order to bring more clearity, why not to consider adding:
Price/unit - but NOT this one which is right now. Why the price which is under the title "Your stocks" is changing? It is the price per one stock which you bought stocks so it need to be fixed price. Ofc it changes when you averaging stocks by buying more. Then price is changing. But you should always compare in easy way your averaged price of stocks to the price which is currently on the market (this one next to the name of stocks).
Purchase cost - I guess it is an overall cost of all stocks which you bought. Ofc it should stay as it is. (Little digression :strange is that it isn't moving! It should because in your model price per unit under "Your stocks" is changing) To improve that you can add something like "Overall current value" which will be current price of stocks multiplied by quantity of your stocks. This way you could easy compare the overall cost of your investment in particular company to the current market value of the company.
The idea of price dropping and going up when you selling or buing stocks is great because it meets real conditions but if you want to go that direction you can't add more stock just like that, from thin air. You should explain the way of adding more stocks and do that rare if you want to keep real life term. Maybe something like additional emissions whose players will be informed ealier could do the job.
During the round you can make some refreshments in the stock market by making initial public offering (IPO) of new comapny.

I hope everything is clear and open for discussion
Regards