You're right, Gilbert - there are so many new people joining SfEP every month, many with no experience, who are willing to work for low rates, and that keeps prices low.
Having said that, most publishers pay low rates - especially today when many publishers use Indian-based project managers. The PMs have to have their cut too.
Proofreading student theses is one way of earning money - but I actually find it hard. First, many students have ESL and this can make it hard to work out what they mean. Second, you have to stick by their university's code of practice re using editors/proofreaders - some unis will only let you proofread a student's work, not change text, you can't change/check references, etc.
Businesses and self-publishing are both growing areas for editing/proofreading though - think about your subject specialties/things you know about. This can be your USP. Then contact businesses in those areas.
But first you need to find out if proofreading is for you. SfEP runs a one-day introduction to proofreading course for people who are thinking about changing career. Then after that you will need training - there's a lot more to proofing than just spotting typos and having good grammar. SfEP offers reputable training.
Offering to proofread for companies on a voluntary basis is a good idea, but I'd recommend getting some experience first so you know what you're looking for.
Being freelance doesn't always fit in with family life - you think and hope it will, but I often work evenings and weekends - so it's not perfect. But I do take time off in the week to go to the kids' school events and help out at school too, so it's not all bad.
PM me if you'd like to ask anything off-forum.