If you're just learning, the M1 would be a decent choice. You might also want to consider an E-MU Emax II. You can usually find one on Ebay for about $200US, or even on Ebay.co.uk for a bit less (depending on the current conversion rate). You may even want to look at the Ensoniq ASR-10, also on Ebay.co.uk.

The added benefit with the Emax II or ASR-10 is that you can have all the Korg M1 sounds in a jiff, as both have full sampling capability.

ASR-10 is a bit more expensive, but it's a much more modern unit. However, for nostalgia's sake, the Emax II was used on TONS of music from the early 90's on.