Recently I buy from Ebay
USB to RS232 Serial 9Pin Cable Adapter For PDA GPS
If URL above is not working you can reffer to Seller is "abcdeshop" and item is in the attachment.
It was cheap $1 and shipping $2.55 from Honk Kong to USA. Come in the envelope with mini CD (drivers). Installing to PC was easy. Appears as additional COM port.
not work with Vixen - Ren-c (Framing led ON). I try it on 2 different PC and same answer - Framing. I test my Ren-c with embedded serial port on one of those PC and got blinking-dimming. 2 days spend to make that USB->Serial comes with no success.
Maybe its working on low speeds and good for serial mause ? Who knows. I did not have any other serial device around. However Ebay seller agree to refund for it (without asking to send back) ;)
I think all those cheap from China and Hong Kong which are for ~$1 - $3 are similar and not suitable for DIYC !