Q How much does a new water heater cost
A It ranges depending on the type, size, and quality of the unit.  You must also take into account installation costs, and other misc expenses.
Q When do  I need to replace my water heater
A Most units have a lifespan of around 5 years.
Q How do I know if my water heater has a pilot light
A If you have a gas water heater, your unit probably has a pilot light.
Q How do I light my pilot light
A Consult your owners manual, but usually you will just depress the button to PILOT, light the flame with a match, and hold the button down for 10 seconds.  If you release the button and the flame is still lit then you are finished.  If the flame goes out, you must wait longer for the switch to heat up.  This is a saftey feature that will close the valve if no flame is present.