Another "Not a plumber" but a DIYer, weighing in, "if" you have to go the tile floor/replace the drain route, I just did this in my basement which we are currently working to finish (and in preparation for my new fish tank). We had to move the rough in plumbing which necessitated breaking up the old concrete, cutting the existing abs plumbing, and re-running/moving the toilet and shower drain. It wasn't fun by any means but it was completed in a weekend (probably take someone who knows what they are doing several hours

) Anyway, wasn't too horrible, re-ran pipe, put in a 3 piece shower drain (one where you lay a sloped bed of cement, then cover that with pvc membrane, then a topcoat of cement, then tile) and now have the toilet and shower where we want/need them. If I had it to do over, I'd go the same direction and I guesstimate (googled a little bit) it saved us maybe 1K+ in costs.
As a side note, to break out the cement where you are working, we rented a Hammer Drill from HD and outlined (with holes in the cement) around the toilet and shower drains, once we figured which direction the pipes ran, we then punched holes in the concrete to where the drains needed to go, and then broke it out with a concrete chisel and the hammer drill. Then dig a trench, lay new ABS pipe, check for slope, glue and back fill with dirt, then finally lay in new concrete.
Hopefully there is a solution to just replacing the cast iron drain
