Anccer (fulfilled by Amazon) has the Ultra-Thin iPhone X case (multiple colors) for $4.07 after using coupon code H2F4UZ5I . Case reviews score "A" at Fakespot. Anccer is also offering a free tempered glass screen protector, click on the "1 Applicable Promotion":
"1 free items on purchase of 1 items
Receive 1 Tempered Glass Screen Protector free when you purchase 1 or more Qualifying items offered by Anccer. Here's how (restrictions apply)"
You can add both to cart from the promotion link described above, or add the screen protector separately. Total of $15.78 for both items becomes $4.07 with Prime free shipping (without Prime, there is a shipping charge if order is under $25) after case coupon and screen protector promotion.