If you are in UK then try ArcEuroTrade for their selection of motors.
As I say I use the 220Ncm motors - and I think there is an offer on them at the moment - my last ones were only £21. They are certainly powerful when wired in series.
Gecko drives you can get direct from the US - but watch dear Alistair Darlings import tax. If you have a friend in the states can post you one, that would be a lot cheaper - my worked out about £70.