Target offers the Outdoor Decor 54x96" Escape Stripe Indoor/Outdoor Grommet Top Sheer Curtain Panel in Blue, Green, or Khaki for $18.99. Coupon code "LABORDAY" cuts it to $17.09. With $6.71 for shipping (choose "Premium Delivery" in cart), that's the lowest total price we could find by $12. It's water-repellant, UV-blocking, and mildew-resistant. Deal ends September 5.
Of note, it's also available in 54x84" in Blue or Green from $23.08 with free shipping, after coupon.