prices and discounts

I'm trying to solve a problem for a client.

It's a language school.

They have, courses so I have a Courses model and table.

Each course has a name and a description and a price_per_week field (a
base price if you like).All is fine, or should I say, was fine.The
client now wants to charge different prices depending on the length of
the students course.

e.g.

1-2 weeks - price_per_week * 1.0
3-4 weeks - price_per_week * 0.9
5-6 weeks - price_per_week * 0.8
7-8 weeks - price_per_week * 0.7
8 weeks+ - price_per_week * 0.6

anybody shed any light on this one? Is my approach sound?