Timing belt replacement takes 2.8 hours multiply this by the labor rate for your labor cost.
The belt is 42.95 MSRP
Tension arm (optional) is 75.82 MSRP
Tension pulley (optional) is 30.92 MSRP
Water pump is external so you don't have to worry about replaceing that unless there is a problem with it.
If your shops labor rate is 70$ and you just get a simple belt replacement (belt only) it should cost 238.95 plus tax.
I looked up the labor and parts cost in the Motor Parts and Labor Guide, I only reported what it said.
If your shop gave you a different price maybe they are replacing the tensioner and pulley. Or their labor rate is higher then the one I gave you (as an example).
Shops however can charge what ever they want it is up to you if you want to pay what they are saying they will charge you in their estimate ,or take your car somewhere else.
Please post back if you need further assistance.