Ask them how many labor hours is required for the job and what their labor rate is. Ask them what your cost on the actual radiator is. The reason they are changing the belt is it will be much easier to do while the radiator is out, and its probably showing some wear. Serpentine belts cost normally now 25.00 to 70.00 depending on how wide and long the belt is, and what brand they use. Goodyear makes a very good belt. Add on replacing both hoses, plus possibly the heater hoses, flushing it out, plus the cost of new safe for cats and environment coolant and the price will be up there quite a bit. 1k sounds a tad high, but simply asking the shop for a detailed estimate that you can take to another shop (or post up on here) will help you a lot in finding out why its so much. But honestly if they are doing all the work they should do in order to properly do the job its going to cost a bit to do it.
