I have never ordered from this site, but noticed they were offering 20% off of AOP SOS...may be worth a look! I think the discount runs only through April. http://www.pennywiselearning.com/Switched-On-Schoolhouse.html
I found rainbowresource.com through someone on this site (THANK YOU!) and their price seems to be about the same as the 20% off plus they offer free shipping on orders over $150 I believe.