I think the best thing to do is find the type of carpet/tiles/bathroom whatever you want to consider. Then cost up the price with just those for the relevant sizes. That will give you a figure without any labour or extra bits for actually fitting them in.
If that figure on it's own is easily manageable then you should be ok. If not, then likely you will either not be able to afford it, or only afford it with the very cheapest materials (which probably won't stand the test of time very well).
From memory our bathroom is budgeted at 100 bath, 100 loo, 100 sink, 200 shower, 100 shower screen, 200 tiles, 250 floor (small but expensive flooring). So that leaves just shy of a grand for taps and labour, and random bits like grout. So the amount of labour seems key to me. We're planning on getting pretty plain stuff from wickes