What exactly you would like to see is what you get as your budget.
It is a matter of value and not money that is available now.
You can carry out basic deco for walls ceiling and floor, or you may also remove some partition and re layout to suit your future needs
As you flat is so small, do you intend to rent it out for decoration or for one person living in and decoration to suit personal style? So Would you like to send me some photos to
[email protected] to check it out for you?
Those quoted estimates in others answers are quite a market prices ranges.
So think more carefully what suits you best and give me a e-mail.