I got the rebate at the airport, it was a tidy sum, can't remember how much I got as we spent it all on duty frees for the group. I think you have to get it from point of departure.
Well worth doing,lots more than £9. and Yes craft knitteds are good value, but avoid the thin machine made ones, get thick hand knits away from Reykjavik.
We were in a group spending about £60 each a night on food and drink and for a group of 5 over 2 weeks, incl gifts, fuel, etc it soon mounts up!
Unfortunately ships are a money-making prison.
I think you could get a voucher to redeem at your bank instead of cash.
I'll look out the info.