Many people have mentioned a quite or silent workplace which is often not only impossible but is actually almost as bad as a noisy one. I can't stand utter silence, it's creepy, so here is my inexpensive suggestion:

A white/pink noise generator

Like a clock that has a white/pink noise generator in it. A lot of them have additional sounds but the beaches have annoying bird noises and rivers make me have to pee so the best ones are the sound modes that simulate rain. My favorite is rain on a tin roof.