When GF4 cards finally hit the market, u probably wont be able to find anymore GF3 cards out anymore... In anticipation of releasing their GF4, Nvidia has already stopped shipping the GF3 chip around a month ago...
So all the GF3's u see in stores out there are just the store's stock... once those are gone, they wont get anymore except GF4...
So my guess is GF3 prices wont really drop that much... if u wanna get a cheap video card though, u might wanna look at the Radeon 8500... the price of that one will remain approx. the same when GF4 comes out, but it will have 128MB memory instead of 64MB!