Installing jenkins and adding a job that will work immediately is a matter of minutes and doesn't require you to touch any configuration file at all.
Definitely much quicker than figuring out the pricing and limitations of CircleCI.
Unless you already have experience setting up a JVM stack, it's going to take you many hours.
apt-get install jenkins
How you'd spend 'many hours' on that is beyond me.
I have a strong feeling someone is trolling here.
Can you paste some of these 'cryptic error messages' that you were getting?
Then you have many platform specific packages or you can just download the war and run "java -jar jenkins.war".