Is it a must to have a serial port these days? Surely it isn't! I thought at the rawest level it's only 0's and 1's.
I use a (AU$40) Dontronics USB converter. At the old end of the scale I plug into our TI555 (Siemens) TiSoft programed PLC, a number of S5's using IBH software and even the old Mitsi F series using Medoc software. As well as all our later PLC's including USB to RS232 then out to TTY, PPI, MPI, DF-1, RS-422 etc.
I have however had big problems with a cheap E-Bay converter.