Ian,

I assume even though he's on a budget he still wants it to be competetive?

You can run the parkflyer hpx f on 7.4v without much problem and they are pretty fast. They aren't the cheapest ones but they are reasonably easy to modify with a bit of superglue and a 6mm drill bit.

http://www.sussex-model-centre.co.uk/sh ... sp?id=4718

They're a bit bigger than micro servos but you can still get comfortably in weight. with something which will flip rather than lift another antweight.

Andy