I'll have to ask my son what he paid for the hardware we used to build his Murphy bed. I know it was nowhere near what you have stated.
The size you are building is larger than any bed, even a king size bed. You might want to lighten the framing. I used 36" hollow core doors to build my layout on, but they are in a fixed position. It allowed me to have no framing underneath. You don't need to use framing lumber to lay the plywood on. A better and much lighter material would be to use 1" x 4" white pine boards to build the frame, then apply the plywood.
With a lighter system you can forgo the Murphy bed hardware and simply use a couple of standard hinges and maybe a cable/pulley system to lift the layout when you are not using it. You will need some sort of latch to keep it in the raised position.
If you are not going to have all sorts of scenery like plaster mountains and such, I can't see the entire platform weighing much more than a hundred pounds.
