Costs vary depending on what your case needs: the work required, length of time and seniority of barrister. Fees can be a fixed amount for agreed upon work or an hourly rate with a set limit so you don’t go over an agreed upon budget. Generally speaking, the more work involved/longer the case will take/more senior (and thus experienced) the barrister, the higher the cost is likely to be.
More information can be found here.