My old and only bathroom is about 8x8 squares. I planned to replace
everything: bathtub, toilet, sink, cabinet, vanity, floor and ceramic
tiles, and new sideboards, prep but no paint. All standard. There
will be very little plumbing since everything will be in the same
place as original.

What range is reasonable for this kind of work? Three contractors
gave me very different estimates: $8000, $17000, and $12000.
Anything I need to be concern of going with the lowest?