If Apple wanted a minority share they could buy shares on the open market and it would likely be cheaper than negotiating a premium over common shares with Tesla.
Depends how many shares but your probably right unless it was for more than 10% I would guesstimate...buying more than that of TSLA in the open market I think would generate a higher stock price unless it was done over a long period of time...wait a minute...what if that is whats happening right now???