Runs on standard batteries?

First of all, sorry if I'm asking a common question....

I'm going on a month-long expedition to Ecuador in the summer, and I want an MP3 player to take. I won't have access to a PC, so it can't use USB, and I won't have much access to mains, so it can't use a charger. I need one that will run on standard AA or AAA batteries.
Ideally, it will have a capacity of at least 2 GB, or take memory cards instead.
I don't want anything fancy, no radio, no microphone, etc, just play some music. And I don't want to pay much more than £40.
I've been looking around for a while now, and I can't find what I'm looking for. Am I being too fussy or has someone got the answer?!