I wouldn't recommend spending a lot of money....try this sale at Prufrock:
http://giftedissues.davidsongifted....47/Prufrock_web_only_sale.html#Post44647Also, Singaporemaths.com check out their clearance, there are some science books.
We did this last year and it was great.
The Marine Science books are pretty good and at $.99 a piece you could get one for each daughter at two different grade levels.
I really like Aleks math for your DD9. You can start at level three, but move her up anytime you like, there is a lot of overlap between 3 and 4. The program generates great progress report and you can customize the reports to synch up to your state's standards.
Make it fun! My girls loved it last year, we'll do a variety of things this year as well. At least an hour, otherwise, they get bored and into too much trouble.

Neato