I recently got back from Siberia and was using a North Face Dark Star -40. -25/-30C temps outside the tent and was toasty warm. Climashield also should last longer than other insulations, though perhaps pack a bit larger than the Lamina bags. I had to import mine from America but it was on sale and I probably paid around £160 with taxes.
Depends what you need and where you live. For jackets and boots etc go to a store. For hardware consider small stores like V12 or Joe Brown's in Llanberis, always nice to help them out and they have online websites too.