Pantou is the code name for the OpenFlow 1.0 software release for the OpenWrt platform. It can be used with a variety of wireless routers supported by the OpenWrt project, and allows you to get an OpenFlow-enabled device with less than $100. Look at the release notes regarding supported devices, upgrade process and other details.
This is an alpha release but should be good enough to start experimenting with. We welcome any feedback to help us towards a stable release!