How do I reject a job offer after I said I agreed to be working at the company?

I didn't sign the contract yet… But now a day after the job interview I'm pretty sure I don't want to be working there. The pay is low and I have to pay my own public transportation. It feels like I will just be losing money. They didn't mention the salary until I asked for it during the job interview… I think for a reason.. How do I politely decline after I said during the job interview I would agree to be working there?