Hi Rik
firstly, no matter where you purchase Merino or Icebreaker gear were over here it is expensive. What will make it good for you is the exchange rate when changing your pounds to dollars. Several well respected outlets here in Christchurch and throughout the Island.
If you are a member of the AA go to your local office and they may be able to furnish you with a copy of our AA South Island Accommodation Guide. If not go to
www.aatravel.co.nz.
As for the route, well, just go for it! So much to see and do in our South Island. But for whats it worth the Catlins, Haast Pass and Inland Road between Waipara and Kaikoura are built for riding.