I'd suggest trying out the swiftech mcp350 as your DC pump. Gary at builtisolar has been
using one for a while now and has been very pleased with its performance. Plus, its cheap at only $55. Newegg.com has them, I'm sure you can buy them elsewhere too.
I've also started a project to make a
DIY thermal differential controller as a cheap solution for the $130+ commercial units. Mine should cost less than half of that. Not absolutely necessary for a PV driven pump design, but it does make the setup more efficient.