Right now, according to Bloomberg, Musk has about $3 billion in readily accessible cash. So he would have to finance the rest of the deal some other way, whether that is selling shares of Tesla or borrowing money.
Musk owns about 173 million Tesla shares. However, securities filings show that 88 million of them are being used to back personal loans. Still, he has the option to buy 60 million more shares, the filings show.