The only way to get a genuine license of Asset CleanUp Pro is this pricing page - https://www.gabelivan.com/items/wp-asset-cleanup-pro/ - as anyone else selling it would do it illegally and you will not get any updates or paid support which you would normally do if you purchase a plugin from a legitimate source. Some websites even distribute free Asset CleanUp Pro nulled versions that might contain malware and it's recommended to stay away from using any of those versions.