supply and demand rules. If you want it so bad now, you have to pay the premium price. As soon as everyone stops buying the 5850 at 300+, the price will drop.
And to be honest, which fool would sell a product for 200 if people are willing to pay 300 for it too and it's not even ripping them off compared to the other products. It's all about what others think your card is worth.
When everyone who can't live without one have one, the prices will settle and I will buy mine between the 100-200 mark. No point in spending more.