If you really want to get your hands dirty you can use
CrystalSpace to create your little game. It's a rather neat little open-source 3D engine. You'll just have to get your animator to help you out with creating some 3D models/sprites.
Much of the stuff needed to create anything is open-source. It's you can use Quake map engines to create your maps (free). Same with the models (this requires a modelling program). Having all the background done for you allows you to focus more on the game aspect of it.
I've been wanting to play with this little gem for a while but haven't found the time...