In a business context, 諮詢費 should be translated as consultancy fee in my opinion. Consultation fee sounds more like a charge for seeing a doctor. Any thoughts?
I've added consulting fee and consultancy fee, though in my experience consulting fee/consultation fee are much more common. Thanks for the feedback!
Nice to see a reply of a mod.
咨询费多少 is what I would feel inclined to use in conversation. The "是" feels a little stiff, but this is a business unit, so perhaps the formality is by design.
Is the 是 necessary?
Colloquially, not. Linguistically, not sure.
It sounds a bit abrupt and rude without it.