Where would be the cheapest place to buy 100+ feet of OFC TRUE 4 gauge wire? I'm starting up a small car audio installation setup and I figure 4 gauge is a nice universal size to use unless someone has a large amp. Your average person won't need any larger.
Also, make sure it's something that's nice and flexible... I don't want to try and do installs for people with wire that's about as flexible as a steel pipe