If you want to keep costs down I suggest:
Buy all materials yourself or the trades will mark up on products - Toilet, basin, cupboards, shower enclosure, bath, tiles, grout, water proofing paint, towel rail, mirror etc etc.
Then ask the plumber what his day rate is - if he's expensive, ask another plumber what his day rate is.
A tiler may be cheaper than a plumber - get a quote for the tiling separately from a tiler, he'll probably get it done in one day.
Get day rates not a quote for the full job.
We renovate property, to make money to survive we either have to do it ourself or wait for a quote. Just recently we are having a wall removed, our first quote was 18k, our second quote was 6k our 3rd was 5k we have found someone to do it for 2k - there was no difference in qualifications or experience in these builders, they just like to try it on.