The Lowes in S. Baton Rouge still offers Contact sensors for $19.99 and free shipping if you spend over $50 before coupon discount. Change your store location after you click the link below:
Even though Renovopower.com no longer has coupons, you can use this code: 47000RRRRR4982R. Replace R with random numbers. You may have to try a few times. Of course, YMMV. I tried it and it worked for me.