If it is for dance, do you mean variable tempo (so you can change the speed of the beat without affecting the tune)? Or do you just mean variable speed (so you can speed up the beat but it makes the tune higher)? Or do you actually mean variable pitch (so that you can make the tune higher or lower without changing the beat)?
The middle one is cheap, the first (which is useful for dancers) and last (which is useful for singers) often come together but are not cheap. Sorry have to run, be back later.
I've got a Panasonic vari-speed CD player but it doesn't take ipod. I bought it 10 years ago and its still going but when we looked to replacing it with an ipod version they were very expensive. The problem is we need it to be able to fill a school hall with sound with the associated background noise of 15 children dancing.
We got it from here http://www.portogram.co.uk/Small-Audio-Systems/
We havealso used http://www.sound-dynamics.co.uk/?cPath=40 for stuff in the past