Screeding the whole floor with maybe an inch of fine concrete is the easiest solution, but this obviously raises the whole floor hight, so doors etc may need to be altered.
The best solution is to remove it and reconcrete, It should break up easily with a sledge hammer or Kango breaker.
Remove the old floor, Then level underneath as much as possible, put down a thin layer of soft sand (25mm) then layout a waterproof membrane (Visqueen 1200gauge polythene). Pour in new readymix concrete to the required hight and level off. Fixing a level wooden batten around the walls will give you a guide to work off to get a completely level surface. You can then have a layer of black bitumen ashphalt poured on or alternatively hire a rotating polisher which will give the concrete a very smooth finish.
I appreciate you are a bit skint, we were exactly the same when we did ours, but its one of those jobs that it might be worth saving up or leaving something else and doing it right before you move in, Its much harder to do once you are living there and have carpets and furniture to deal with
Hope this helps
Steve