Weme via Amazon offers its Weme 5-Foot USB to RS-232 DB9 Serial Adapter Cable, model no. LYSB00ZL2SRZW-ELECTRNCS, for $9.99. Coupon code "6BOQEYG9" drops the price to $4.99. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $8.19.) That's the lowest total price we could find by $10. It features a Prolific PL-2303AR chipset and thumbscrews.