Based on your description, the pipe goes into the basement, and then out under a slab floor. My guess is that it is 4" cast iron. Is this correct?
A couple of questions.
How many toilets on this drain line?
How straight is the pipe? I take it there is a cleanout in the basement, so if you take it out, is the pipe nice and straight under the concrete floor?
If the line is reasonably straight, and there aren't more than 2 toilets on this piep, I would see if you can push a piece of 3" sch 40 plastic pipe through the inside of the 4" pipe out to the outside of the house. Dig down on the outside, cut a section out of the pipe and transition back to the 4" line. Inside the house, cut the cast iron off flush with the wall, and repipe as necessary to connect to the line. It would be best to take 3" all the way to the toilets, but it isn't really necessary if you use a tapered fitting instead of a straight fitting from 4" down to 3".
It might be best to install low flush toilets as well, but probably not necessary. It would be best to make the transition in a vertical section of pipe or fairly steeply sloped horizontal section if possible.
If that isn't possible, I would run a complete new line before digging up that kitchen floor. That is a major undertaking!
It really isn't that hard to dig a hole large enough to get a new pipe through right under the concrete, assuming that the dirt isn't full of rocks or other debris. Knock a hole in the concrete wall, say 6" diameter or 8"x8" (1/2 block) and start digging horizontally with a tile spade. You can strap longer lengths of wood to the spade as you get deeper and just keep going, bringing the dirt back into the basement.
You can also dig in part way from the outside, maybe 4' so you only have to go 8' or so. I've put dug as far as 14'+ under sidwalks and bushes doing this, and it actually works quite well.
Push the new pipe through, make the connections, seal the hole in the foundation, and your done. Much easier and less mess then tearing up your kitchen floor.
