Is iWork free ?

Provided that you already have macOS Mojave (10.14.6), or Catalina (10.15.n) installed, then you can download Pages, Numbers and Keynote versions 10.1 from the Mac App Store application on your Mac. Otherwise, you cannot download these current applications.

Yes, the individual iWork programs are free. Here’s how to access them:

1. If you’re on a Mac that is able access the App Store, click the App Store icon.
2. Next, the App Store window will appear. Near the top is the search bar.
3. In the search bar window, type Keynote and hit Return on your keyboard.
4. A list of apps will appear. Select the Keynote app, and click Install.

Repeat to download Pages and Numbers.

Happy creating!

LearningAgent

Apple no longer offers the iWork '08, or '09 DVD for sale or component download. These were never free applications, and in early Fall 2013, Apple shut down the registration servers necessary to convert (pay) from the trialware timeout to full versions.

You can purchase non-trial iWork '08 and '09 DVD from Ebay resellers, or do without. Apple is out of the loop on this.

This would be true if the OP was actually running Mojave or later, but as was clearly stated, El Capitan is installed, and that nixes current Pages, Numbers, and Keynote applications.

Also, the OP has the trial version of Pages '08, and wanted to continue using it for free, which is not going to happen, because the trial has timed out, and the (paid) activation servers have been gone for almost seven years.

Pay attention to the details before jumping in with answers.

Yes, and you get what you pay for.