I have a 1-bathrom home that I'd like to turn into a 2-bathroom. I have engouh space in the existing bathroom to comfortably split it in half. All of the plumbing and electrical is easy other than adding a toilet. Here's the existing layout (left) and my proposed layout.

One option to reduce the amount of concrete cutting is to put the new toilet on the left against the exterior wall but I doubt I would have enough fall the the sewerage lines (which extend from behind the existing toilet to the right).

I have pictures of the build so I know exactly where everything is.

I would be very keen to hear from anyone who's had this kind of work done in the past. I don't know if I'm looking at more like $20k or more like $80k. The former I can stomach, not so much the latter. I'm going for a lower-mid-range fitout, the only cost I'm really concerned about is the concrete cutting and repairing for drainage.