Unless you already own a vintage DOS laptop with a real serial port and a Motorola RIB, you will spend more time and money getting the software to run than paying a dealer.
If the search for is leading to too many headaches, consider these alternatives: Motorola Gm350 Programming Software Download
: Hosts legacy Motorola software ZIP files, including wgm350.zip for the GM350. Unless you already own a vintage DOS laptop