That seems reasonable for the dealer to charge. I'm sure they're making plenty off the sale of the loader too, though.
Some things that would make it challenging for an individual to install a loader are the weight of the components and the torque that has to be applied to the mounting bolts. The mounting brackets that are installed on the tractor can be pretty big. The brackets on my Kubota 1153 loader (on M7040SUD tractor) are probably over 150lbs a piece. They're different on every tractor, with some probably being quite a bit heavier. Handling something like that could be a challenge. And the bolts mounting the bracket to the tractor are torqued to between 250 to over 400lbs, on different tractors. It's not impossible to put that much torque on something at home, but doing it somewhat accurately could be a challenge.
For the amount of money you're paying for the tractor and loader, why not spend a couple hundred more to make sure it's installed correctly and you don't damage something trying to install the loader.