why are you going for 2 wide lenses out of interest?
though you said you had a 15mm prime?
Have you used this?Prices seem a lot more uniform recently though, have got excellent deals from my local shop even without having to pricematch. Have also used DigitalRev in Hong Kong though even the savings there aren't so big anymore. Worth it if you spend £600 plus though.
quite heavy though
the sigma 12-24 is big and heavy as its designed for 35mm frame. The other lenses aren't usable on 35mm