Dick's Sporting Goods offers the Lady Hagen Women's Essential Long Sleeve Golf Polo in several colors (White pictured) for $17.50 with free shipping. That's $18 off and the lowest price we could find, outside fo the mention below. It's available in select sizes from XS to XL.

Note: Golf Galaxy has it in sizes XS and S for an in-cart price of $6.39 plus $5.99 for shipping.