I am not even talking about money, I am more concerned about which one is more similar to the real exam and also to J2EE 1.6 topics (Annotations, Assynchronous and so on), that are pretty difficult to find questions about these topics on internet.
I would recommend you to go for free mock exams. You don't need to prefer these paid exams. Just read Servlet specification 3.0 thoroughly. It covers everything.
I passed this certification last week with 85% without any paid mock exams and it is not at all difficult. Only HFSJ and servlet specification are enough to crack it.
Talking about annotations, just go through all the annotations and their usage. They mostly ask usage of annotations. I did not face any question on asynchronous. So go through asynchronous topic from servlet specification 3.0, it will be enough.