To start with, I would propose that your pricing is all wrong from the beginning. Charging per page is like charging for a pound of material, regardless of what the material is. Would you charge the same for say a pound of topsoil as for a pound of gold?
You can now tell your client that over the year your pricing structure has changed and that you now charge based on multiple factors. Then provide a quote based on what it will take to create the store, its functions, and the value it brings to the site.
If you need help understanding how to charge feel free to contact me at info@ssgconsulting.com