A second guinea pig doesn't take up any more room than 1, the minimum cage size for 1 is the same as 2. It also doesn't really add up to much more regarding food either. Guinea pigs are like people, even ones that arent fussed about others of their own species still thrive having at least one other to speak to and hear, even if they dont share a cage. It would be like waking up one morning to find no other humans on earth, it would very soon start to affect your mental health, as like guinea pigs, we're hard wired to be around others.