How much it will cost to repair depends on where the leak is at. To try to figure that out on your own will take time. What you need to do is isolate different parts of your pool and continue the bucket test while doing so. Was your pump running overnight during this most recent test?
What I would do is perform the bucket test, but before doing so, turn off the pumping system and plug all your return and suction lines at the pool. That is, cap off returns and bottom skimmer holes with screw in or expandable plugs. What you are attempting to do is isolate the pool from the pumping system. Then do the bucket test. If you lose no water, you know the leak is in your plumbing, not the pool. If you do lose water, you know it's in the pool or skimmer area, not the plumbing. It's much like any troubleshooting procedure. Isolate different parts of the problem system until you narrow down the issue.