With all due respect to "December M," do NOT follow that advice. Preventive maintenance is always better (and less expensive) than corrective maintenance. The flat rate for changing the timing belt is 4.6 hours. Find a reputable garage that will do the work, check them out with the Better Business Bureau, and try to find one with the lowest labor rate. At $100/hr, the labot would be $460.00. The price for the timing belt may be somewhere near $175 - $200.
Should the timing belt break while the engine is running, engine damage wold most likely occur and the cost would be well above the replacement of just the tiing belt.
Good luck.