Im willing to bet that many many people would have bought the PS3 if was that priced, but the wii would still have done very well, simply because of the casual audience.
Furthermore, if the PS3 released at 299.99, Sony's entertainment division would've lost so much money, they would've gone bankrupt, and would be in a worse position than today. Lets just say 5 million extra people would've bought the PS3, that is not worth being multiple billion dollars in the hole. That would not be a sustainble 10 year plan.
There is a reason they released the PS3 at the price. You think Sony wanted to release it that much? What you are suggesting would probably have destroyed them.
To the topic, I would've bought the wii, because I have a 2000 dollar gaming PC.
Edit - A better question would've been. How many people who bought the 360 would've bought the PS3 at that price.