You engine is an interference engine. What this means is that when the timing belt breaks the valves in the cylinder head crash into the tops of the engine pistons which results in bent valves and possible damage to pistons and the engine cylinder head.
As far as repair costs- it is going to depend on extent of damage. You have 2 cylinder heads on your vehicle.
If both need to be replaced with new valves, you are going to be looking at around $1500-2000 parts and labor.
If pistons were damaged and the engine needs to be overhauled on the lower end as well as new heads, you can looking at $3-4500 depending on extent of lower engine damage.
If engine needs to be replaced, that can vary widely on whether you get a factory engine, a remanufactured engine, or an used engine - prices will go from $4000-7000 parts and labor.
But, before you panic, the first step is for the mechanic to remove the heads and have them inspected for bent valves, cracked head, and inspect pistons for damage.
If any damage is found- ask to see it before ok'ing any repair. Some techs automatically assume on these engines that when the belt breaks that the worst has happened without actually checking. I have seen some people get lucky and no damage occur- doesnt happen often, but on occasion if your speed wasnt very high when it broke, then you might not have any damage.