There you will see Starter and Enterprise tabs:
Please note that by default, Starter plans are available for purchase on the annual basis, so if you'd like to switch to the monthly billing, make sure to set the tumbler to "off":
You can find the plan comparison on this page.
If you'd like to start with the trial first, please note that you will be billed after 2 weeks or after exceeding the trial quota (500,000 characters). However, you can cancel the trial at any time before.