As per Dave, I have a range from ATS from 6mm up to 120mm probably 20 different sizes, if you look after them properly they will easily last for half a dozen bathrooms. A basic set of 6 or so sizes will cover most scenarios say, 6,7,18,25,30 and 45mm, they'll only cost a tenner or so for those few and you can add a few sizes more if you need to.
120mm @Bri Jeez how much did that set you back? I just mark my hole with an off cut of pipe and lay the grinder into it.