1996 Saturn SL1 Cracked radiator, overheated, now engine pr

Hi, I was driving two days ago and suddenly the thermostat and coolant level lights (above the coolant temperature gauge) started flashing. I topped up the coolant and that sorted the problem for the remainder of my short journey. The next day I drove a couple of miles and the lights came on again and the car overheated. I left the car parked up overnight, and when I returned to it, it had lost about half a gallon of coolant! I topped it up again and drove it to the nearest garage. They said the radiator was cracked, and replaced the radiator and both hoses, as well as a new thermostat. When they ran the engine after doing the work, they noticed that the engine was misfiring so they did a compression test. Apparently 3 of my cylinders are giving a reading of 120psi, and one of them is giving a reading of 70psi. Apparently I need a valve job, which will cost over $1000 (much more than I paid for the car). Repairing the car for this sort of money is not an option. I wondered if any of you had any thoughts on what the problem is and what caused it. Does this sound like a head gasket problem? Or some other engine problem? The mechanic said he wasn't sure and would need to take it apart to find out. There doesn't seem to be any white smoke coming out of my exhaust, well maybe a tiny bit. I have done a bit of research, and some people in a similar position to me have used engine block sealer to fix any small cracks that might be inside the engine. Also, if one of my cylinders isn't working properly should I disconnect the spark plug for that cylinder? From what I have read some people have driven thousands of miles on only 3 working cyclinders, other people say that you should definitely not do this. Any thoughts would be appreciated. Even if I could hang onto this car for a year then that would be good, as I can't afford to buy a new one.