To this point I have made maybe two dozen hive boxes and the frames to fill them. I have a hard time imagining making 850 frames at once. It gets monotonous cutting out 50 at a time. The top and bottom bar machining is pretty straightforward but it would take me several evenings. It's the 1700 side parts that would drive me bananas. After you rip the 850 pieces of lumber, bevel one side 1700 times and make jigs to cut 3400 slots top and bottom you will stand at your router table for another week cutting the material off the sides 3400 times.
I don't know that they are more trouble than they are worth but at that scale I might rather spend the $558 to buy 900 frames. However, if I am short by only a couple of boxes and have a weekend to spare I'll be making sawdust in the garage. Plus, as Mr. Bush says, it allows opportunity for experimentation and possibly improvement.
...boxes out of 2x lumber? Maybe for an overwintered nuc. I happen to have a few boards of southern yellow pine laying around...