The economics of nine hole courses are a lot better than many assume. If water and power are readily available and there is existing road access to the site, a nine holer can be built for under 60% of an eighteen holer. As Adrian notes, you can't build half a pump house or purchase half a control system, but you can halve your pipe and wire and drainage elements which make up the lion's share of the irrigation budget. On the revenue side, players are willing to pay 60-70% of an eighteen hole rate for the opportunity to play nine. On the expense side, the right people need to be found. Find a superintendent who likes to be on the ground rather than behind a desk and a versatile pro (or manager) not averse to managing all aspects of the operation, from budgeting to ordering to banking to player service to teaching to flipping the odd burger or serving a beverage from time to time. They're out there. The whole operation can be made surprisingly lean and flat. Although rounds capacity during the busiest times can't match half an eighteen holer, expenses can be managed to below half in slower times.
Finally, it's a mistake to equate "nine" to "short". The scale of a nine holer can be and should be made every bit as big as an eighteen holer.