Need a new way to charge customers .. help!

I charge a 'minimum' charge which includes up to X pages.
This could change depending on the client. So I would have an idea on what sort of information they want to display and come up with roughly how many pages that would be then I would put a flat rate in the quote for these pages and then give them another price for each additional page.
eg: $600 including up to 5 pages of layout/coding.
$70 per additional page
or something like that.
But there is no option to 'delete' pages to reduce that base rate.

Instead of charnging $300-400 for 'graphic design' I would ditch that and just have one amount which includes graphic design, web layout etc of up to x pages. Additional pages at $x