I can remember before the boom, DW 1 fetched $35-$55, DW 2 fetched $130-$175, and DW 3 & 4 traded for $250-$400 each. DW 1 hasn't seen much of an increase (it's only up to $45-$60), but I can see DW 2 in the $300-$400 range, DW 3 in the $400-$500 range, and DW 4 in the $500-$700 range. Those two listings were the first of either to see eBay in a good long while, to my knowledge, so that probably played a role in them selling for that much.
It was steep, but I needed DWII to finish my sealed DW set. I hadn't seen one in a while (passed on one a long time ago), and finally decided just to go for it. The same seller also sold a DWIII and DWIV to the same buyer, though apparently as side deal. I know this because this buyer, seeing later that I had won the DWII a few days prior, contacted me to see if I would consider selling him the DWII I had just won.
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http://cgi.ebay.com/Nes-Nintendo-Dragon-Warrior-IV-Factory-sealed-Ultra-R_W0QQitemZ270204399480QQihZ017QQcategoryZ62053QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
These are crazy prices imo, not sure about DW1 (don't think its worth that much) or DW3
I'm not sure about DW II & III. Would say $150-$250 for DW II and $300-$450 for DW III.
Dragon Warrior IV can probably hit a bit less than $1000, but it depends on the buyer.