Different side menus for different pages

Here’s what I’d do:

Create a different page template for each side menu that you want to use: COPY your default page template, page.php, and be sure to EDIT THE COMMENTED PORTION AT THE TOP to give your new page a unique name (perhaps something to do with the different sidebar), just anything to jog your memory about the page.

For each different sidebar, I’d just hardcode the sidebar contents into that page. If you do this, be sure to remove this code:

<?php get_sidebar(); ?> from your template if it exists.

(I guess you could use PHP includes and create separate sidebars, and THEN call those into each page template, but why? Especially if the OP doesn’t have that many different sidebars.)

When you want to create a new page, you should be able to select it from a drop-down list in the Write Page area.