I reckon they should be about £200 at Xmas, it will be 6 months or so after launch, the market will be ripe, they'll probably be selling the GF3 Ultra then and will also have competition from the other major players and hopefully some titles to better implement the technology of the card. It just feels like it's going to be the best time to get a new card.
Of course, you could just get one now if you think that a £100 saving is worth 4 months gameplay, look at it like your spending £25/month to rent one until Xmas. If that seems too steep then ride out your MX until Santa comes .
If you've got your money for nothing, who cares if the chicks are free!