Google are now encouraging people to create an ad campaign and enter billing info, before they can use their Keyword Planner tool.
But the trick is to not go too far into the process and you can still use the tool free of charge.
On the 1st screen click the link that says 'Skip the guided set-up' - see visual below:
Then you will have access to the keyword planner.
If you do go beyond this stage, don’t worry. You can always set your campaign to paused, and you won’t get charged.