There are really only 4 main things this could be.
Battery can't put out the amps to crank it. (have it checked with a load tester)
Autozone and such other places can do this for you as well as some battery sales places.
We have a Budget Batteries store that does it, and I'm pretty sure Interstate battery houses also do.
The connections must all be clean and tight (especially if you have those temp terminals)
For fixing cable ends.
Make sure you have good clean and tight connections, and a good ground from the battery, to the body and especially from the battery to the engine.
The relay (which you jumped to bypass but still had the same problem so probably not the relay)
The starter, because the brushes can get worn down to where they don't make a good contact on the starter armature to make it turn when power is applied.
This one is fairly easy to diagnose.
When it just clicks, smack the end farthest from the engine a decent whack with the hammer and try it again.
If the hammer smack made it work again, then it is for sure the starter.
While there make sure the starter is bolted down tight. (it can't ground well if it isn't, and can cause the same symptoms.)
After all this is done IT WILL TURN OVER or you will find why it doesn't.