If you are looking for an more environmentally friendly alternative to sunlight soap that doesn't cost $10 a bar then try Ecostore bar soaps. I picked up one for about $1.80 from New World. They are a bit smaller than the average bar soap so to get the same amount as 1/2 a bar of sunlight soap (as required in this recipe) you will need almost a whole bar (60g out of a total of 80g to be exact, use scales is my advice).
Now, they do contain palm oil and I have given Ecostore a lot of flak in the past about their use of so called 'sustainable' palm oil. But recently Ecostore have been using a programme called GreenPalm. This is how their website describes the programme:
"Ecostore supports the production of sustainable palm oil through the GreenPalm programme. This means that for every tonne of palm oil/palm kernel oil we use in the production of ecostore products we have paid a voluntary premium to a palm oil producer which is operating within the Roundtable on Sustainable Palm oil’s (RSPO) strict guidelines for social and environmental responsibility." - http://www.ecostore.co.nz/about/palmoil.html
This is a major improvement from Ecostore's previous policy ('we're a member of RSPO so it's all ok') but it still relies on the RSPO definitions and policies on what 'sustainable' palm oil is (which are not ideal) and on their auditing system (which, from what I've read is practically non-existent). More on the RSPO here.
So as far as I see it, GreenPalm certified palm oil is a big improvement and I think it is good enough to be supported as a step in the right direction, but it should not stop there!