Woot offers LectroSound White Noise Machine for Sleep and Relaxation for $9.99 (orig. $24.95) with free shipping with Prime.

Note: If you're a Prime member, you'll get an additional $3 off at checkout. Just make sure you log in using the Login with Amazon button.

Product Description:
LectroSound does one thing, and it does it well: providing whitenoise for sound masking and promoting better rest, relaxation, andsleep. The tone dial provides precise control of the sound's warmthacross the spectrum of brown, white, and pink variations. You can alsoadjust the output with the volume control to match the needs of yourenvironment. It's USB powered and does not include an AC adapter for usewith wall outlets.

• Personalize your sleep experience with the perfect sleep sound
• During the day, it's great for masking sounds for increase privacy and focus
• Works any powered USB port
• Easy to take with you, whether it's across the room or across the country
• Warm, robust, truly random white noise at an affordable price
• Does not included USB to AC wall adapter