Call some of the block casters around. They run test runs of various styles at different times, and then sell them off cheap when they don't have a customer for the test run. I got mine from Boral Best Block on the south edge of Denver.
I bought these for $1.50/ea, and used them to completely redo my backyard. These would be total overkill for your project, but they were great for me where I ended up with a wall that was 5' tall at it's highest point. The down side? Each one of these weighs 100lbs, and they use fiberglass pins to connect the layers. The pins made great work of keeping them located, but they added some cost.
First layer and yard carnage by
ARNEWB, on Flickr
Wall mostly assembled by
ARNEWB, on Flickr
These are actually spec'd and used for highway overpass retaining walls and such, but for the price, I couldn't beat it.