I think I've found the perfect sleeping bag! 640 grams!
It fits the temperature range nicely and is rated to an extreme of -4 degrees...but I would be hoping not to be anywhere that cold.
The Vango Venom 150:
Suggested Usage: +7 to +25oC
Performance: 2 season
Maximum User Height: 185 cm
Dimensions: Length 210/ Chest Width 75/ Foot Width 50 cm
Total Weight: 640g (Excl sac 575g)
Fill Weight: 1x90 top/ 1x60 base g/m2
Pack Size: 20x12 cm
ebay has them on buy it now for about $169 + $10PH
UK shops have them for about 50-65 pounds which would be cheaper but postage tends to be hefty...
Jackson online (a UK store) have it for about 160 including postage.
Outdoor Action have it for about $130 including postage from the UK...