TomTop offers the Habotese Electric Socket Tester for $7.29 $9.49. Coupon code "WDUS" cuts that to $6.79. With free shipping, that's the lowest price we could find by $7. It features a small LCD. Deal ends October 31.
Note: This item ships from China and may take up to four weeks to arrive.
None of these moves requires a big investment, and they all can save you money.