I wouldn't pay that, but probably not out of line for a shop. In my opinion they aren't that hard to rebuild, if you just pay attention to what you are doing and are somewhat mechanically inclined. My suggestion is to start with one carb, take pictures or whatever you need to do to remember how it came apart, and tear it down and start the rebuild. IF you get stuck on where something went, then start the 2nd, until you get the 1st back together, then finish the 2nd, if stuck again, start the 3rd, by this time you should have a pretty good idea of what you are doing! I'd buy some chem tool or something to soak them in to clean out all passages, then blow them with air to insure they are clean. I wouldn't say I'm an expert, but I've successfully rebuilt the carbs on my E-150 XP and my Johnson 50hp, as well as a few jetski carbs.
Once rebuild and on the boat, I pay the local shop about $100 to have them tune them! Some people are patient enough to figure that out, I'm not one of them! I don't like messing with stuff on the water!! Plus, if they tune them, I know they are right!!
Good luck!!