Do you think that GPUs will now start costing less, with less people buying them?
No. It is clear we aren't even 1% of AMD sales, even AMD can confirm that. The bitcoin community is incredibly tiny. It may seem like there are a lot of people into Bitcoin if you are like me and read about it all the time, subscribed to the subreddits, on this forum, see it in the news, etc. It's just not that big of a community, though.
The price of used GPU's might go down directly on this forum, though.
used 5970's were $400 each on ebay two months ago, now they are $200
i'm pretty sure that's bitcoin related
as for new cards, if not for bitcoins, i'd buy a geforce card, ofc they'll drop in price