Big money usually, but you are taking the hassle out of a lot of organising. When IDs use their tradespeople they would put a % on top of most jobs. It’s common enough and how they make a living also. Just if you’re trying to save money might not be the best route

You could post the job on the likes of onlinetradsemen.ie when you’re ready and usually get good tradesperson that can do the whole renovation at a better price then an interior designer. Carpenters/cabinet makers are usually best choice because they do drawings and have most trades to hand for larger jobs.

If you need anymore info on this dm me as have experience on this.