Does this tile quote sound right?

We have a tiny hall bathroom with a 4X5 area of floor space that we want tiled. My contractor asked me to pick out and purchase the tiles and supplies. I bought 20 square feet (plus some extra for breakage) plus grout and sealer. The floor is exposed now. The vanity and toilet had already been removed. I believe he put the "backer board" (is that what it's called?) down today. He told me it would cost me $600 to tile the 4X5 area. I was not expecting that. I bought 41/2 inch black and white tiles for a simple checkerboard pattern. He said it is so high because of the pattern I chose and the fact that he has to go around a toilet and that he doesn't know how the tile will adhere to the paper on the board (that is already on the floor). We don't know a whole lot about this but we seem to have a pattern of being taken advantage of from the workers that come in our home. I'm trying to prevent it again and I do plan on getting some more quotes from tile contractors in the area.