dang, forgot to update the thread, but we found and fixed the problem (well, "we" as in the mechanic)
The mechanic changed the starter and tested the other parts, but everything was fine. Then they decided to test the battery cable itself and they saw that it was damaged inside. I dont know exactly where it was damaged, but it wasnt near the terminal parts, because my dad and I had checked that before and it had seemed ok. I wasnt there when they pulled out the cable and replaced it, my dad was.
this sucks. Now the car works again for a couple months and then a new problem will pop up. The cycle never ends, and my occasionally-dimwitted father keeps pouring money into it.