No. DMX is a different animal than serial RS-232.
I'm cheap too. Even though the dongle has some expensive components it is much cheaper than the alternative: Enttec DMX pro at $155
There are some other options for DMX that have the computer generating the DMX stream but one little blip in windows and the stream becomes corrupt. The Lynx dongle does the work of generating the DMX stream (512 channels @ 255 levels of intensity each 40 times per second. Regardless of how many channels you are using all 512 get sent every 25ms) and the computer only has to tell it what changes.
Chris