Walmart offers the Ozark Trail Outdoor Chair Umbrella Attachment in Blue or Red, model no. WB-001 for $5.97. Choose in-store pickup to dodge the $4.97 shipping fee. That's tied with our January mention as the lowest price we've seen. (It's a current best by $13.) It features a clip on the bottom that's compatible with most folding outdoor chairs.

Note that a chair is not included.