Re: why is Gtx 280 generally more expens then gtx 285?
Performance wise the gtx 285 only wins by a small margin. However, it is cheaper to make due to the 55nm die. This means they can sell it for cheaper and maintain their profit margin. Different brands will also price differently depending on things like warranties, coolers, overclocks brand name etc.
So you will find that a 280 will almost always be cheaper than a 285 of the same brand.
That being said, if you can find a cheap gtx295, get it.