I though of a cheaper option:
NMEA Starter Kit #124-69 and
Lowrance NAC-MRD2MBL NMEA Network Adapter Cable #127-04
$84 shipped
NMEA Starter Kit #124-69 details:
Network starter kit. Includes 2 terminating resistors (TR-120M-RD, TR-120F-RD), two T-connectors (N2K-T-RD), one 2 ft extension cable (N2KEXT-2RD), and one 15 ft extension cable (N2KEXT-15RD), and a power node (N2K-PWR-RD).
For use with all Red network devices.
Compatible With: GlobalMap 5200C, GlobalMap 5300C iGPS, GlobalMap 7200C, GlobalMap 7300C HD, GlobalMap 8200C, GlobalMap 8300C HD, GlobalMap 9200C, GlobalMap 9300C HD, HDS-10, HDS-10m, HDS-5, HDS-5m, HDS-5x, HDS-7, HDS-7m, HDS-8, HDS-8m, LCX-112C, LCX-113C HD, LCX-37C, LCX-38C HD, LMS-520C, LMS-522C iGPS, LMS-525C DF