it entirely depends on whether you want to move things around, how large the space is, how expensive the tiles and fittings you chose are.
Broadly though I generally budget for spending as much on labour as you have on the tiles, fittings, flooring, decoration etc.
My last one (a small child's en suite cost £2,500 for everything but it was a poor job). My current one is nearly finished - its the main en suite for the master bedroom (about 11sqm) and its costing £15k. So its a how long is a piece of string question really.