[hcobb]

If the point is to make beginners progress faster...

The first memory point is 100 XPs.
The second memory point is 200 XPs.
The third memory point is 300 XPs.
The fourth memory point is 400 XPs.
The fifth memory point is 500 XPs.
The sixth memory point is 600 XPs.

And so on.

Note that this would balance against wizards since they spend the most memory points. (This would be 100 XP fewer at the 10th memory point, then a higher cost thereafter.)