TomTop offers the Mini Fruit Ukelele in several styles (Kiwi pictured) for $6.99. Coupon code "WDLL" drops it to $4.96. With free shipping, that's the lowest price we could find by a buck. This plastic ukelele has four strings.

Note: This item ships from China and may take two to six weeks to arrive. The countdown timer on the product page does not reflect an actual expiration time and resets daily.