Too easy.
Here's one breakdown:
So it looks to me like:
125 x $1
100 x $5
25 x $25
---------------
250 chips
would be plenty for 6 people, $100 buyin with 6 rebuys.
If you want to support $200 buyins and rebuys, just buy 50 more $25 chips:
125 x $1
100 x $5
75 x $25
----------------
300 chips
If you're going to buy 400 - 500 chips, you can have much more flexibility in your games. Which way would you like to go? More players? Different games (limit, tourney, etc) Different stakes?