A lot depends on the materials you choose. If you are choosing tile that is $6 a foot, your price is significantly higher than $2 a foot. I had a bare concrete floor and stud in my master bath that is around 120 square ft. I used a claw foot tub that was in another bathroom.
For plumbing, I used PEX and sharkbite with plastic piping. Incidentally, I plumbed the house in about 6 hours using this system(kitchen, laundry, one bath and one exterior spigot, along with connections in water closet for second bath).
The tile, I ordered an inexpensive tile saw off Amazon, and used the hell out of it. I found some nice 18x18 tile on sale at Home Depot for $.99 a square foot. I bought extra because I knew I would mess some up. The wife chose a nice tile to go with the floor tile for the shower. It is 18x18 as well. If you are going to build a concrete floor pan, google it and good luck. I just couldn't bring myself to try it yet.
For small jobs, you would probably be best off finding a handyman. Some prices I have seen by contractors around here I thought were ridiculous. It is why I do most of my own work, even if I have to learn it and buy the tools.