When I made my 50ft extension cord, I bought a 50ft 10/3 welder extension cord on e-bay, cut the ends off and installed RV 30 amp connectors. Cord and connectors, I think I have $75 in it. Now that I carry it in the MH, I'm betting I will never need it. :-)
NOTE - I prefer to carry multi purpose components - I'm thinking about making a couple short adapters that I can plug into this cord and they'll have alligator clips on the ends, This would give me a 50ft long jumper cable. I've needed that a couple times. :-)
2001 Coachmen Mirada (Ford F53 6.8L V10) - Toad 2001 Civic
It won't do MACH 2, but I can get a sandwich and take a pee.