What do you use the 280GB 900P for in front of your 1TB drives? You're right the bottleneck is often somewhere else in the system once you have modern SSDs. The 280GB 900P is ~$0.89/GB [1] and 1TB EX920 is ~$0.15/GB [2] these days, so the cost delta is not an order of magnitude (i.e. >10x).
What's funny to me is that the first consumer flash SSDs Intel released were just over 10 years ago, and they were ~$7.44/GB with only 80GB capacities [3]. Things change quickly, eh?