I use
Marpac's SleepMate / SoundScreen (it's the same unit with two different names). I see their prices have gone up a bit since I bought mine (I think I paid like $30).
It has a fan inside a plastic case that allows you to adjust the volume/pitch of the white noise (by adjusting the amount of air going in/out). It's louder than a typical fan would be, but probably quieter than most of the electronic variety. I bought mine about 4 years ago and it's still running just fine.
jHE