I'm pretty sure they don't plant a brand new golf course every time the president wants to play so you amortize that upfront cost over the expected lifespan of the golf course. And the president probably has a set of clubs he likes rather than demanding new gold plated ones for every hole. And the entire time he's on the course he's arms reach away from whatever important crap comes up.
A typical 18 hole, par 72 golf course is 150 acres of high quality land. Enough land for 150 McMansions if it were put to such use. So even though there is a huge upfront cost, there is a continuing opportunity cost. Furthermore, the maintenance costs are very high, probably running into the $1 million to $2 million per year range for courses which Obama wouldn't even deign to play.
Regardless, it's unnecessary to grind through the calculations because all of the information we need about consumption is contained in the greens fees. Obama has been playing
here. The greens fees are $170 per person per round. Not an extravagant cost to be sure, at least relative to the cost of staying on Martha's Vineyard in the summer to begin with, but certainly beyond the means of the vast majority of Americans.
The time it takes is probably the greatest luxury. Yes, some golfers (and usually non-golfer supporters of golfers) claim that they can do business on the golf course, and so it's not a total waste of time. Putting aside the fact that Obama primarily golfs with non-politicians and non-policy makers, so that rationalization rings a little hollow in his case, I can tell you from personal experience that it is not so easy to discuss business on a golf course.
The four-some is together for only two phases of the play: tee-off and final play on the green. Most of the time is spent far away from each other on the fairway, or (usually) looking for balls in the rough. And during the tee-off people are usually discussing how to play the hole, and during putting on the green, people are either discussing how to play the green or are quiet. After the hole is finished, people generally talk about the hole that was just played. The bottom line is that doing business on a golf course is largely a myth. It's a boondoggle for the express purpose of doing fun stuff while pretending to work.
Which is not to say that I begrudge Obama his time on the golf course. I can't imagine that there is a better use of his time anyway, unless there are some drone strikes that need his approval. And, as you point out, his advisers know where to find him if some Presidential decisions are needed. Of course, his decision may turn on whether or not he just missed an easy putt, but I'm sure a lot of Presidential decisions are similarly arbitrary.