We use the graupner speed 900 with good effect. Bit large and heavy with 660 gram each, but very powerfull and efficient for a low RPM (6000 rpm @12V) and good pricetag £20-25 if bought over here.
But the Graupner speed 720 BB torque could also be a good option.

For batteries, if you go pusher, I would take the Hopf Sanyo 3700 sub C NiMH in the 12V 2*5 stick pack cells. £20+P&P per pack.