How do you correlate the Size of the bunker to the maintenance cost? If I had 18 pot bunkers that had to be maintained by hand, that would be more expensive than 18 shallow ribbon bunkers that could be quickly machine raked. Or high, sand faced bunkers vs frying pan sand with grass faces. At $100/rnd, bunker maintenance cost is not the driving factor.
BTW, we did a course that had a 4.5 acre bunker. It came into play on 4 holes. It was also pretty easy to maintain because it's size allowed for a large, tractor driven dragmat setup that was about 3 sand pros wide.
However, I do believe that a quality course could be achieved under such parameters. But, it is hard to look at the spectrum of Hazards and just single out one form. We also have streams, burns, ponds, lakes, trees, ravines, etc.to consider.