[GreenKeys] Current loop to RS-232 converter?

[Charles Morris]

Is there any inexpensive current loop to RS-232 converter available? I 
used to use one of my 33 ASR's with a PDP-8 which I've since sold, so no 
longer need current loop. My other retrocomputing hardware is 
sufficiently modern  😉 that RS-232 interfaces are all I need.

I could build one by hand, but I'm feeling lazy ;) Vince Slyngstad and I 
designed and built a PC board years ago, which is still running in the 
other 33. The expensive part of that one was the small DC-DC converters 
to run off the 48 volt TTY internal supply.

The prices for off-the-shelf interfaces today are astounding, in the 
neighborhood of $150-200! Forget that.
Anyway, suggestions welcome.
thanks
Charles