Direct from Moto you would need the cable and a RIB (Radio Interface Box - sits between the PC and radio, ribless cables have the components of the RIB built into them)
- RIB - RLN4008: $200
- Cable - RKN4035: $227.85 (<-- I'm not 100% sure this is the right one, you might want to call motorola and ask)
- You would also need a DB9 to DB25 cable to connect the RIB to the PC, you can get these real cheap online or from a store like Micro Center
Total: $427.85 + $279 for CPS = $706.85 (Insane, right?)
I have heard also that the RIBs from PolarisUSA.com work well.