2001 Mustang GT starting problem

2001 Ford Mustang GT 4.6 5Speed 53,000 mi.
While on a road trip the car badly overheated and I didnt notice until smoke came pouring from under the hood. After pulling over we found the coolant boiling out of the overflow tank. After letting the engine cool we replaced the thermostat (although I feared of more extensive damage) and everything worked fine. I drove the car another 100 miles and everything worked fine. The car started and ran fine the next day, but the day after that as I was about to return home the car wouldnt start. There were no leaks at all. The car sounds like it wants to start and tries to turn over but it just wont catch. I checked all fuses and relays, the fuel cutoff switch, and they were fine. The fuel pump doesnt turn on when the ignition is on and there is no pressure on the fuel injectors. We thought it was the fuel pump but a neighbor mechanic came over and said the reason for it not starting is a cracked cylinder head. My question is could the car run fine for two days and just not start the next day with a cracked cylinder head or head gasket with no leaks at all under the car? About how much would it cost to fix it? I have had the car less than a week. It really sucks. Thanks in advance for your help