I need two serial ports (RS-232) and an MCU already mounted in a box. This is not something that requires an OS, so Arduino level is fine. It is going to read in serial data on one port (9,600 bps) and spit it out again with a bit of reformatting. The input data is a 50 character burst every 1 second.
I figure the unit will run from a 5V wall wart.
I've looked at Digikey, Mouser and done numerous web searches. The closest I could find are not really programmable units, but serial port "servers".
If I could program these, $100 would be the right price.