Brand new about £55 each.
From a fellow roboteer - not sure on the price. but under £35.
Ian - go on what Alan just said, up to 14.4v is a decent speed and power on the normal plastic gears, then if you want, use 24v on a brass gear, long as ther kept well cool.
But saying that- DTK has still hmm lets say damaged a few brass gears running on 24v still. But oh well - things happen.

Mr Stu