By cheap, I take it you mean less than $139. Let us know if you find anything.

I have one IOGear GUC232A single port adapter. For a while I thought I saw these on-line for $19, but the lowest price I see now is $29. At $19, 3-4 of these might have been one of the cheapest option if you had a cheap USB hub kicking around.

This has been a frustrating area for me. I have an Intel (nee Xircom, nee Entrega) 4-port RS-232 hub that *may* work under Windows 98 that I can sell you!! (but it never really worked...)