From my completely non-scientific from-memory-and-instinct analysis I reckon that pricing is $400 for a 10GB Mk2a, +$50 per 10GB, -$50 if it is a Mk2, +/- $50 random market fluctuation.
Not enough Mk1s come up for sale to really know how much the pricing differs. One the one hand they are more limited in memory and functionality, but on the other hand they have some sentimental appeal.