Dohairx via eBay offers this Two Color-Changing LED Bike Valve Stems for $1.20 with free shipping. That's the lowest total price we could find by $2, outside of the mention below. It's compatible with US and UK valves. Note that it ships from mainland China and may take three to eight weeks to arrive.
A close price: Sparkling Star via Amazon offers a similar item for $1.50 with free shipping.