A ton of folks at Artscape were really interested in the homemade laundry soap. I really enjoy using it because:
1. Making the soap in bulk is cheaper than buying it from the store (and it's less money to companies making tons of chemical products)
2. Less chemicals, dyes, and perfumes
3. You can reuse the same plastic container over and over, instead of buying a new one each month.
Here is a link to a site with great tips, troubleshooting questions, and price breakdown (although she did manage to find cheaper supplies, but it is an older website so perhaps prices have gone up...) http://www.thefamilyhomestead.com/laundrysoap.htm
And here is the site where I purchased my laundry soap kit: http://www.soapsgonebuy.com
I was a cheap-ass and bought the less expensive kit with full bars of soap instead of the pre-grated kind. I'd say go ahead and splurge on the pre-grated, because Fels Naptha is a really hard soap, and grating it is really not that fun. Even if you do it while watching t.v.
There is another option too: I have seen Borax and Washing Soda in the laundry aisle at the Giant in Hampden (in the Rotunda). Your grocery store might have it too, or you might be able to get them to order it for you. Then you won't have to pay any shipping and handling fees.
One last tip: I am probably going to switch from Fels Naptha to a more natural castile soap (like Dr. Bronners). I found out after I bought all the soap that Fels Naptha does have a petroleum based solvent in it, according to Wikipedia: http://en.wikipedia.org/wiki/Fels-Naptha. Castile soap is more expensive, but it will be worth it.
Although Fels Naptha does have another interesting use as poison ivy relief, and doesn't seem to bother this woman with sensitive skin.
Let me know how your experiments turn out!
If all goes well, I may have a table at a farmer's market in the future since lots of people are interested in this product, but not everyone has the time to make it.