Thats probably close to what your going to pay anywhere Greg. A lot of the price charge is taking out the old refrigerant which is very costly.
If you have any friends that do any HVAC work you might be able to beer them..... I mean talk them into hooking you up for a reasonable offer.
There is a little more to the switchover also. Oil adding, new o-rings, stuff that sounds minimally invasive but costly. You might be able to find out how to do it online? DIY?
In a pinch you might even be able to check someplace like Jiffy-Lube who also do that type of work for cars, just to at least get a secondary price. It can't be any different than a car.