The cheapest off-the-shelf solution I can think of is a wire.
RS422/485 is differential, with both active high and active low
outputs and inputs. RS232 is active high, in contrast to the
UART serial data itself, which is active low.

IF you have a single RS422 device to talk to, AND you're using
a PC or similar device, THEN you can connect the active-high
422 output to the PC data in (pin 2 on a DB9 connector). For
the input side, connect the active-high RS422 input to the
PC data out (pin 3 on a DB9 connector). Connect the other
RS422 input to a pair of resistors, so that it sits at about
2.5 volts. If you can get to the RS422 interface chip, there
should be a 5V and ground connection over on the other side
of the chip. You just want to set the unused input pin at a
potential that's in the middle, so that the driven input will
swing higher and lower than the un-driven input. These things
have differential inputs, you see.....

For most all modern PCs, dating clear back to the early days,
the RS232 transceivers recognize about 0.8/2.0 volt guaranteed
thresholds. That means you can use them at 5 volts and ground,
with some degradation in noise immunity.

This still works for multi-drop communication, so long as the
PC is the master. RS232 has no provision for multiple-mastering
the line, so although the slaves can share a line talking to
the PC, the PC won't let go of the line to let somebody else talk.

RS232 output levels are typically 10-12 volts, but the RS422
transceivers I'm familiar with can all handle about 15V without
any problem.

Failing that, there is always the sure-fire method; power supply,
regulator, RS232-to-5V chip (MAX232), 5V-to-RS422/485 chip (MAX490)
and a couple of connectors. Or you can buy something from the
Black Box guys, all packaged and done.

http://www.blackbox.com/catalog/index.htm

Mark G. Forbes, R & D Engineer  |  Acres Gaming, Inc.    (541) 766-2515
KC7LZD                          |  815 NW 9th Street     (541) 753-7524 fax
forbesm@peak.org                |  Corvallis, OR 97330
http://www.peak.org/~forbesm
mforbes@hq.acresgaming.com

"There has been an alarming increase in the number of things I know nothing
about."
---Anomalous