You might be able to get paid work in a hospital - I'm a Health Care Assistant in my holidays, and although I don't work in the mental health bit, it is possible to get extra training to allow you to do this. However, you'd need to be applying for this with a view to either working all year round, or during your holidays (if they're long enough to make it worthwhile), as they don't take people just for summer etc.
It's so annoying that the best work experience to do (summer placements etc) are unpaid. I'd love to do some, but I just can't afford to take a month off work!