I really admire Kent Wang & Sunspel's offerings (Sunspel 'sRiviera polos are sometimes available under $100 in certain colors & sizes), though I don't own any. John Smedley is highly recommended and infrequently available under $100 if you search. Typically I wear polos in very casual settings & prefer J .Crew's garment-dyed slub cotton polos, for comfort & low price. Perhaps obviously, Polo Ralph Lauren & Brooks Brothers are classic; Banana Republic has some nice-looking polo sweaters around your price point, as well.