Well if his 9% actually appreciates over time (by no means guaranteed), then the only real cost is any opportunity cost of using the money for this right now.

Well if his 9% actually appreciates over time (by no means guaranteed), then the only real cost is any opportunity cost of using the money for this right now. Which, given the investment environment, may not be that large. So assuming that his stake grows in value over the long run, it's a very small cost, really.