Jon:
You make a good point and though we have gotten side tracked a bit, I think one has to consider the cost of drainage at the outset and how best to approach it to achieve success in a reasonable manner. I am all for drainage when needed based on good common sense and practical civil analysis, but digging a trench say for a 12", 18" or 24" main line 2.5' deep as Ray R. indicates can work and keep costs manageable. At this depth the walls of the trench should support themselves and the laborers can work within a normal bucket width from an excavator at that depth, but digging a line 5'-6' feet deep as you noted changes the cost outcome and the physical act of doing so considerably.
Once you get past about 4 ' and especially at 5'-6', you'll likely need trench support for the walls to prevent collapse depending on soil type and that will cost more $. When digging at 5-6' you are simply moving more soil around and the contractor will charge for this too. At that depth the trench will need to be wider for laborers to have enough room to work, hence more soil to move around and more $. Finally, at 5-6', backfilling and compaction rarely go well--that is to say that few contractors take the time to properly compact the trenches and it never fails to see ugly
settlement after the first 2-3 years. I can tell you that this is a real pain in the ass and it will be difficult to get the contractor back after the 1st year punch list items.
Again, I agree with your premise, but if we are to keep golf affordable, it has to be considered all around from start to finish.