Hi Kari,
If a private company is buying a public company, they are almost certainly taking them private. If they are not, and just want a controlling stake, they need >50% of the shares.
In both scenarios, the purchasing company will never have a share price.
In terms of the acquired company, the acquisition cost will be [# shares] X [price per share] X [some % factor higher]. This is because the share price represents the most recent trade but not all trades require to get the desired # of shares.
If you've studied economics, you'll know that there is a supply/demand curve. As such, any additional purchase of shares will have to be made at a higher price than the current market rate. The case should guide you on this, but it could be anywhere from 10-50% higher than the market rate (on average).
Thank you Francesco !