Chevy cylinders

I have a 2005 Cheverolet Classic ( malibu) Automatic that has about 52000 miles. My car didnt turn on after I turned it off to go inside my house for about 30 minutes. I tried to jump start it up it didn't work, I then took the battery to get it checked and it wasn't no good. So I bought a new one and replaced it. My car still didn't turn on. I had a diagnosis done and it came out to have low compression: 1) 180 psi 2)15psi 3)25psi 4)30psi. What does this mean. The mecanic said he has to open the engine and see what happened. He charged me $1,550 to fix it. Does this sound right? I'm a student and I cant afford this so i'm trying to fix it myself. Haha If you could suggest anything I wold appreciate it. Thanks!