StarTech.com Serial DB9 RS232 Extender over Cat 5 - Up to 3300 ft (1000 meters) - serial port extender

The RS232EXTC1GB Serial over Cat 5 Extender allows you to increase the distance of your RS232 Serial connection by up to 1000 meters (3300 feet), giving you the ability to connect serial peripheral devices up to a kilometer away from your system - an incredible 65x greater than normal RS232 serial cable length restrictions would permit.

Price: 124.78 from Currys Business