Does anyone know what the going rate for tutors is these days?

I'm a primary school teacher with a masters in special ed. I am contemplating taking on some tutoring whilst on maternity leave but have no idea what to charge. When I was at Uni (almost 10 years ago), I was getting $20-25 an hour so I would assume rates have risen by now, just not sure how much.

EDIT - I don't want to overcharge by any means, but I don't want to sell myself short either.