I've been told that one of the reasons RAM is so expensive now is that about five years ago the memory manufacturers mis-judged the market and built too many manufacturing plants. For about three years prices were in the basement, everyone was losing money, and some companies (TI was one of them, weren't they?) got out of the market completely. No one was building new production capacity because everyone was just treading water.
In the last year, with increasing sales of PCs, MP3 players, PDAs and cell phones, the market for memory has improved. But because no one was expanding their manufacturing infrastructure over the previous few years, we have a memory shortage.