Hi, I am a qualified nanny and have worked in London for 15 years. I would say that the best place to start is either childcare.co.uk or nanny job.co.uk . The first you just post a job and can send messages direct to childcare professionals. The second you can also advertise but all the nanny agencies also advertise so might be a good way to get an idea of the agencies in your area. I would say that to get a decent nanny it is definitely not cheap at all depending on your requirements. ( I definitely cost my bosses more than nursery). Hope that helps and that you find someone that works for your family.
Nannies won't be the same price as nursery, not good ones and if you do it properly anyway. One-on-one care isn't the same as a nursery setting.
In our area we have a rural recruitment company which is for nanny's etc. Look for a agency 🙏