“How much does it cost?”MSRNCFresh off his explosive public foray into American politics, SpaceX and Tesla CEO Elon Musk is now posting about buying MSNBC.Responding to misread reports that Comcast plans to put the liberal news network up for sale — when in reality, the broadcaster plans only to spin MSNBC and other brands off into a separate company — Donald Trump, Jr. tagged his famous new friend.”I have the funniest idea ever!!!” the president-elect’s son said in a clear, if joking, reference that the politician scion thinks Musk should buy his…