Bar oil is never 6$ a gallon where I live. 9$ is the cheapest I've ever seen it. A friend of mine who don't burn wood anymore gave me 3 gallons awhile back, so that was great. Nothing wrong with mixing other clean oil with bar oil to stretch your $$. I'm also one who will not run used motor oil for bar oil.
Lack of tackifiers. What exactly is drain oil? Please don't say what came out of the oil pan of a vehicle.