Yesterday I found an option similar to Copyscape Premium without paying .05/search. I remember looking for a Copyscape alternative before opening my premium account last year after some unfortunate incidents with a team member but I didn't find anything that was quite the same. Plagium is the closest thing I've seen so far.
Plagium is a beta tool that's currently free that offers you the ability to check text by URL or by pasting it and it even has an alert feature that you can subscribe to, in order to have the system police for you whether or not someone may be using your content.
For writers, this can help you ensure your work is completely original when you submit to a client and it can help you ensure that no one is stealing your work as well. Plagium can also benefit you if you're someone that buys website content or PLR articles packs for your business as well.
I've been a huge believer in the fact that it is worth .05 cents to protect my reputation and have written about that in the past here on What a Nickel of an Investment Can do for Your Writing Career.
Comparing Plagium to Copyscape Premium
Yesterday I ran a test on a piece of writing I wrote several months ago and got the same results between the tools. Today, I ran a different test and a brand new HubPage I wrote (probably not indexed in Google yet) and published a few days ago and was found on Copyscape but Plagium couldn't find the text. So, I'm not sure that I'll give up my Copyscape account yet as it it definitely worth a nickel to ensure I'm not unintentionally committing the ultimate writing sin but I'd definitely consider using this tool, especially the Plagium alert feature.