Red X Angler
I have found it cheaper to buy jumper cables and cut off the clamps then to buy the cable alone, but you get basic automotive grade wire. 6ga will do what you need. Up to 4ga if you want for the starter but I think 6 would do. I assume we are talking a small outboard (under30hp) and 12v trolling motor? If budget allows use tinned wire and solder ALL connectors to the wire and seal with heat shrink or paint over it good with liquid tape then wrap with tape. You can run it all through pvc pipe for more protection.