If you go: Piriform --> HOME --> LEGAL --> Software License for CCleaner Professional -->
4. UPDATE SERVICES
Subject to your payment of the applicable annual update fees and support fees for the relevant year, Piriform shall from time to time, via its website, make available new versions of the Product for you to download and use (the "Update Services"). Nothing in this Agreement entitles you to receive any support, maintenance, updates, upgrades, content or new versions of the Product, unless you are a paying customer with a current subscription.
So it's not a one-time payment. Just stick to the free version. It's just as good