How do I get floor level over 7m?

That's 7 metres, not miles....by about 3 metres.
Uneven kitchen floor, slopes a bit one side, pitted in places where quarry tiles gouged out, dips a bit where new screed is. I've read post about grinding high spots, filling gouges with 400 mortar and running around with a spirit level, but over 7 metres I can't maintain accuracy.
Do I need to hire a laser thing, and can anyone tell me the method?
Also, two screeded areas seem to have been levelled with a droopy straight edge! So over a 2m run, there's a drop of about <1cm in the middle. I know SLC is expensive, so is there another (cheaper) solution for initial levelling?
Many thanks for your time and help (hopefully assuming someone gives either....).

Thanks.

Just please confirm what you are hoping to achieve...

...is the kitchen already fitted?
...are you looking for smooth blemish free? (easily achievable with screed)
...or billiard table level? (difficult if not impossible)
what will be your eventual floor finish? - LVT, or Vinyl or what?

Thanks for replying! All good questions about what i'm actually planning to do, which only a fool like me would leave out. Planning to put porcelain ceramic tiles down, not too bothered about perfection, kitchen not in place yet. Previously, I put adhesive down and spirit levelled as I went along, and result was very good. Having extended into garage, scale is much bigger so worried I might start too high or low with tiling in this way. Thanks.

Oh- and don't want to raise floor too much- currently 1 to 2 cm below rest of house, so don't want to put thick screed on top if possible. Thanks

Porcelain is slightly out of my area - maybe the tiling forum????

I would imagine that the principle is the same however...

Yes - screed it. It is a large area though good luck with all that mixing!!!!

On further thought maybe you should check with the tilers just in case they reccomend a specific screed.