Walmart literally has you covered at the beach, sidelines, bbq, and more with the Lightspeed Quick 95" x 95" x 59" Canopy with Side Wall for just $69.00, the lowest price I've seen.
If you need something more substantial... as in a full enclosure... you can pick up the very highly rated Coleman 4-Person Instant Tent at a massive 50% off, just $82.44 from Amazon.com.