What causes a timing belt to jump and oil in spark plugs, how much should it cost?

I have a 1997 honda accord 2.2 4 cylinder. It has 305,000 miles on it. I was driving the other day and it worked just fine, all of a sudden it stopped working and my radio was still playing, i check under the hood and the was oil in my spark plugs, people are telling me my timing belt jumped time, what causes it, and how much should it cost? It acts like it wants to crank but it doesn't

Oil in spark plugs could he a head gasket. Timing belts need to be replaced every 100,000 miles for maintenance, especially in Saturn's and hondas. If the timing belt goes, the whole engine goes.
If you have oil in your spark plugs or oil in your coolant, or coolant in your oil, that's a sign of a bad head gasket. Best thing to do is take it to a mechanic that you trust.
Timing belts can be about $1000, depebding in the vehicle, with labor and parts. Its not something you can really do yourself unless you have a timing gun. Even then, its hard.

Oil in the plug hole is a valve cover replacement. I would suspect the timing belt jumped or broke right off. If it did jump then get a t-belt replacement service. Need a diagnosis to be sure. T -belt water pump 700.00. Valve cover replaced 100.00. Get the valves adjusted too.
If it is an interference engine the cost goes up.

At 19 years and 305K miles, I'd guess the cause of your trouble is that the engine and probably the rest of the car is completely worn out and may not be worth fixing. Take the same money and buy a worn out car half that age.

http://autorepair.about.com/

The 305,000 miles likely has everything to do with what happened. Your fix will be at least a grand.

How often did you change the timing belt? On a Honda, I'd do it every 60,000 miles.

I suspect there's more damage than a new belt will take care of and cost of repairs will be more than value of the car.

Don't crank it over. If the belt has jumped you'll damage the valves and Pistons. I'd think that a used engine is your best bet but frankly with this mileage the car is hardly worth fixing.