Ending today, Lands' End takes 50% offfull-price men's, women's, and kids' swimwear via coupon code "STARS" and PIN "9900". Shipping adds $8, but orders of $50 or more bag free shipping. A couple of best bets, with prices after coupon and $8 for shipping:
Smart Buy via eBay offers the Hot Safety Kids' Inflatable Swimming Vest in Orange, Blue, or Yellow for $4.08 with free shipping. That's tied with our mention from a week ago and the lowest total price we could find now by $3. It's available in size S.
Note that sizes M and L are available for slightly more.