Twenty years ago, 4x1mb 72-pin RAM (four megabytes, or 4,194,304 bytes, or 33,554,432 bits) costed me about $100. I have paid similar price for 210mb harddrive. You do the math.
Thirty years ago: Hard drives were not widespread, and memory was counted in kilobytes (so praised Mac had 128mb of RAM, and single floppy). YOu can go to your local library and pull out old editions of BYTE magazine, you will see plenty of ads with prices.