After graduating from university I have just started a non funded PhD in an area I am really interested in. Recently I have turned down offers of interviews for jobs in areas that do not interest me that much. I am now worried that I have made a mistake. Should I be thinking about the money and attend these interviews and gain work experience in my field? Or is it more important to do something I really enjoy and stick with this PhD despite having to worry about money for 3 years?

I would stick with PhD as it is very rare that you get to spend time on a topic that you're really interested and can devote alot of time to it! You won't get this opportunity again even when you get a paid job in the field of your studies as you will have other duties and responsibilities so enjoy it while it lasts! It's a privilege!

Think of it this way - would you rather spend the next 3 yrs having fun doing something you really enjoy & investing in your future career/job prospects or doing a job you're not really interested in just to get some money? You'll get bored of your job if it doesn't stimulate you -trust me on this one! I'm doing work experience on a topic I really enjoy and it's by far the best job I've had and I don't even get paid for it! !

You obiviously seem to enjoy topic so I would go with your original decision. Try to get demonstating/teaching experience as they pay quite well (also good experience if you want to go into academia and for CV.) Try any other uni jobs going also eg. exam invigilation pays quite well. All the best. ; )