If you need more time, after the trial the price renews at £7.99 – but right now you can take advantage of the 42% discount on the 6-month Entertainment Pass. The discount brings the total 6-month price to £27.99, which is roughly £4.66 per month.
Watch Chernobyl online for free with Amazon Channels
In the US, you can also watch the entire first season Chernobyl on Amazon Prime video when you add HBO as an Amazon Channel. With Channels, you pay a separate subscription fee for access to more content. In this case, you'd pay $14.99 per month for HBO. However, Prime Video offers a free 7-day trial for HBO, which means you get a week to watch Chernobyl for free.
See our full guide to Amazon Channels.
If you're not in the US, you could in theory access it using a VPN, but keep in mind this would be against the terms and conditions. You would also need a Prime Video US account.