I hope this issue of down select to 1 goes away. We all know this is a political issue, not financial. For some reason Congress would rather pay higher price for Russian transportation than save money on commercial crew. This has been demonstrated over and over again with cuts to commercial crew, that if original funding had been approved many years ago would probably have resulted in astronaut flights to the ISS now.
Down selecting to one is never cheaper especially after the capital has already been paid to develop two or more systems. With no competition, monopoly price will always increase. If Congress does force a down select to one, it will not be to save money, but to appease companies that support their election campaigns.
Edit: to expand on the statment about "original funding", if full funding had been provided, then NASA would be saving money now by not having to pay the Russians for another 2 years of flights. Overall money would have been saved.
Edit: added funding chart.