It's not like Iran is getting $300B cash. It's a $300B plan for the "reconstruction and economic development" of Iran. The U.S. Treasury would also waive sanctions on oil exports.
Some say that this deal is no better than what Obama had in place. Who knows what we'll end up with after negotiations are complete. It looks like this whole war was for nothing. The disposition of their enriched uranium stockpile still has to be negotiated and they are allowed to keep their current nuclear program in place.
It just made the oil industry a whole lot of money and the defense industry will benefit next as they resupply.