The physical transceivers for RS-232 and RS-485 are different, and thus are not configurable. With regards to the converter, I do not have any specific recommendations, but a quick glance at the B&B Electronics catalog shows a couple of dozen different options that run from $70-$125. Which model you need will depend on the features you're looking for: connectors, max baud rate, surge protection, power source, isolation, etc.