texwelder,

Your Vantage 300 will take a K857-1 (100ft cord) I just got one for my 305D from "weldingsupply.com" on my doorstep for $204.90.  Lincoln has a new cool one that has power on it K2627-2 but there MSR is somewhere around $800.00.  I don't remember exactly because I dropped the phone in shock.  Anyway, that was the best price I could find.