Hello,
Welcome to JEvents! The JEvents core is free an open source. You can see all our changes here:
https://github.com/JEvents/JEvents
We haven't had many security issues, but the problem you face is if you do not update your components/plugins how are we as developers going to know how to fix a security issue with your code which is so old. For instance, if it's a month or two out of date it's likely we could advise how to patch it easily since the lines would match to a point.
If you are say a year out of date and we have re-written hundreds of lines of code with updates and Joomla! compatibility then we just wouldn't know exactly where to start, and to provide a patch for your old out of date version would take us quite a bit of time. And to re-subscribe even if you went to Gold at £70 is the cost of around 1-2hours of a normal UK developers time which really isn't much if security is your concern.
Many thanks
Tony