There are low mileage 2013 Volts out there but the prices are as high as 2014/2015 models (unless you can bargain them down, I got my 2013 for $5,000 less than asking by sticking to my guns as they were "motivated to sell").
Back up cameras were only standard on the Premium Gen1's, optional on the base. If there is no factory back up camera as the is no hole for it you have to add through the back window style (not a good way to go) one so if that's what you want, hold out for it. Aftermarket backup cameras that are better are available for replacing stock ones if that's your thing.