I have a 99 Neon DOHC with approx 130,000 miles. A few months ago it started overheating, so I had the thermostat changed and a new radiator cap ... seemed to cure the problem, but shortly after it developed a leak in the radiator ... so I took it and had a new radiator installed. Not long after that was done, my son did a little off-roading with the Neon so it was tied up at the body shop for most of the winter. Upon getting the car back it was overheating AGAIN! Also ... through most of this ordeal it has always done the gurgling sound when you shut it off. Anyway ... recently my son had the car out and it overheated and shut down ... it has not started since .... just cranks. Someone told me to check the oil and see if it looked "milky" ... Its not milky at all.
My question is ... what are the possible things this could be? And what should I expect to pay for these repairs?
I thank you in advance for any help!!

In order to guess about the problem and cost to fix, we need more info. I do anyway.
The failure to start may not be related to the overheating at all. Have you checked for any 'codes' from the CEL (check engine light)? The light doesnt have to be on all the time for there to be trouble codes stored with useful information. Do you know how to get it to blink-out the trouble codes? Go to the 1st Gen. Neon forum, and open the link for the 1st GEN FAQ's & Read the 5th paragraph. If it blinks out some codes, their meaning is listed at the link in that paragraph. The rest of the FAQ are also good to read for a Neon owner.
Beside a problem with the cam position sensor, with the crankshaft position sensor, with the relays that operate the fuel pump and the oxygen sensors, there are several other things that could keep it from starting.
When you first turn the ignition key on, if you are in a quiet location you should hear the fuel pump hum softly for about 2 seconds. To check whether there is fuel pressure, you can unscrew the plastic cap over the schrader valve located in the middle of the fuel rail (above the intake manifold, but it may be covered by the big wide air inlet plenum), and push in on the valve stem with a nail. Fuel should squirt out, starting at a pressure of about 49 psi. Dont do this with any flames or sparks nearby - it will easily ignite. If it doesnt squirt out for a moment, something is not providing fuel properly. This would prevent it from starting. There are problems with some of the engine sensors that would prevent it from starting - but they should show up as 'codes' from the 'check engine light'.
I dont really have insight as to what would have caused the overheating. I would want to check the camshaft, to make sure it was still in-time with the crankshaft. This isnt easy to check, as the mark for the camshaft positions can be seen okay, but finding the mark for top-dead-center of #1 piston is not easy. Probably the simplest way is to put a wooden dowel rod into the spark plug hole, and let the #1 piston push the rod up as you turn the engine from the vibration damper pulley at the bottom of the car.
You mentioned a gurgling sound when you would turn the car off. I would presume that is boiling coolant, and it should not be doing that. There are two metal tubes running from the motor over to a pair of hoses, that run to the firewall. They take hot water to and from the heater. They also allow water to circulate through the engine head while the motor is still too cool for the thermostat to open. If they have been blocked off - the heater wont work, and the engine head will have some hot spots in it during normal operations.
Im not sure the engine would be shut down by any overheating condition, but if it was, Im sure the beeper would have been chirping away. This is the same annoying beeper you hear when the door is open and the key is in the ignition.
Hopefully someone else will give you better advice; but the first question from most responders will be asking what the knowing what the CEL (check engine light) trouble codes were.
Let us know.....