Macy's takes up to 85% off a selection of men's swimwear, with prices starting from $7.96. Pad your order with a beauty item (they start at $3) to bag free shipping; otherwise, shipping adds $10.95, or get free shipping with orders of $48 or more. A couple of best bets, with comparisons excluding the beauty item padding for free shipping:
Tommy Hilfiger Men's Maison Colorblocked 6.5" Board Shorts for $15.96 (pictured, $54 off)
Speedo Men's Striped 10" Swim Trunks for $17.73 (low by $31)
One grocery chain is likely to save you more money than any other.