TechMatte via Amazon has amCase Clear Bumper Cases for Google Pixel 3a, 3a XL, and more (listed below) for $4.16 each when you apply the corresponding promotion code.
amCase Google Pixel 3a Clear Bumper Case $4.16 with promo code 9LU8UIT7
amCase Google Pixel 3a XL Clear Bumper Case $4.16 with promo code 5RAXFPTT
Also available:
iPhone Xs Max Clear Bumper Case $4.16 with promo code 8TUDYRAK
Samsung Galaxy Note 9 Clear Bumper Case $4.16 with promo code 8TUDYRAK
Samsung Galaxy S10 5G $4.16 with promo code 8TUDYRAK
Samsung Galaxy S10 Plus $4.16 with promo code 8TUDYRAK
Samsung Galaxy S10 $4.16 with promo code 8TUDYRAK
Samsung Galaxy S10E $4.16 with promo code 8TUDYRAK