Personally I'd start by asking around your contacts in the sector you work in to see if they know someone. I work in a pretty niche sector and have never thought it worth my while advertising in directories etc. Most of my work comes through contacts/word of mouth.
LinkedIn can be a useful way to find out some names and explore what people do - try looking at the members of a few relevant industry-related groups - I bet there's a fair few freelance professionals among them.
I need to hire a freelance marketer (ideally with a specific sector focus). Where is the best place to look as I've come across quite a few sites where freelance people can register?
I want to avoid using agencies and their costs.
Don't want to add too many details as I'm aware you can advertise vacancies on Mumsnet and don't want to be accused of advertising a vacancy by stealth. Might give Mumsnet vacancies a go - but just wanted to pick peoples' brains first.