Before I decided on an insulated raft, I was looking at a similar, more traditional, buildup. For a polished finish, then its a "simple" case of concrete screed that is then polished.
I didn't go this route in the end, but really liked some Lazenby floors that I looked at, with jots of different shading options. If I remember correctly it was about £90 - £100 sqr m. for pouring the concrete screed through to polished finish.
It does require expansion gaps though. I think around 30 sqr m, or 6 linear m is about the max they like to do without a split.
Alternate would be a micro-top / micro-screed / skim-coat finish over a standard screed. But I found this was almost as much as a concrete screed, so more money overall.