I am shopping for an MP3 player with dc power and repeat song function?

Can anyone recommend an Mp3 player that has a repeat song function (any song, not entire playlist) and has a DC power in source? I want to have a "white noise" player for my toddler's room so she can sleep through distractions. I want to be able to load my own "white noise" recordings, and I do not want to have to replace batteries or recharge all the time. I only need a small capacity (64MB-256MB). I am hoping to find an used early model for little money. I want to load several "songs" but have the ability to choose different ones to repeat through the night. I know that "sleep machines" are available, but they seem antiquated with the new technology. I want to play a longer loop than most of these do to avoid "repetition". I am talking about recording a babbling brook, a waterfall, or rain -- things like that.