What OS you running? Houdini doesn't run on OSX. I know there's ways to install other OS's on Mac hardware nowadays, but I'm not up on it. One of the bigger stumbling blocks is that OGL support on Macs falls behind the other platforms.
I've heard Rush is pretty good for the bucks. We use Sun Grid Engine here, but in your scenario, to get up and running with the least headaches(and writing the least number of wrappers
), sounds like, apart from OSX, that should do the trick.
Cheers,
J.C.
P.S. If the Mac thing becomes an issue and you're going mini for the costs, then you should look at regular intel render nodes. It's cheap.