92 square feet is roughly 9x10. A 3'x5' sheet of 1/2 Durock from Lowes is $13. You will likely need 7 sheets, or $91 of material. Screws will probably set you back another $20 or so.

1/2" plywood to cover the same room will also be under $100, screws will likely be similar cost.

It does take longer to put down the backer board, but not that much longer for such a small space, maybe an extra hour. BTW, you should put a thin layer of thinset between the backer board and the plywood subfloor so you dont have any air pockets, which will help to stop movement. Movement allows tile to crack.

That was very helpful, thank you. How much would you estimate for installing NuHeat electric radiant heating for the same 92sq ft area? The contractor quoted $2600, which again seems very high.

Back to the original question about changing from ply to cement board... Was the "contractor" originally planning on tiling directly over plywood? If so, thats not typically an approved method. He would need either some sort of backerboard like durock or something like Ditra. I'm pretty sure this guy is taking you to the cleaners.

As for the Nuheat mat, if you're talking about just installation, I would think that is quite pricey. All he would have to do is put down a thin layer of thinset and put the mat down in it. Possibly put a layer of SLC over top of it if he's not using Ditra. He would also have to connect the electrical which depending on the state of your house could be pricey since they should be on their own circuit.

I'd keep an eye on this guy given the information you've provided.

Dan

re. "if you're talking about just installation"
Actually it is materials and installation, and I guess materials run at about $1,150 - $1,575.

For the nuheat get an exact breakdown. Sounds very high. Can you do any of this work yourself? We DIYd a new bath with a warmly yours heated tile floor.

I agree with advertguy2. Sounds like your contractor has some issues. You should never tile directly over plywood. Plywood plus Ditra (or other isolating membrane) and then tile, or plywood/backerboard/tile.

That price also seems too high for installing the heated mat. You basically roll it out, use a little hot glue to fasten it down, and then tile right over it. You could also put a skim coat or self leveling cement down, but you dont have to. The cost of the skim coat or SLC is not very much, and shouldnt take more than a couple hours to get down.

I would get a more specific breakdown from the contractor, and then ask him why the labor is so high for a couple extra hours of work.