I think the simple perspective is the cost of the car in one column and the cost of the marketing / transaction in another column. The value being based on what yer buying - yr, model, options, condition, history - what a reasonable person would pay. The cost of marketing, be it auction fees or ebay fees has absolutely nothing to do with how much the car is worth, it's the amount somebody is willing to spend to find a buyer.

BJ results are the last place I'd look for determining actual real world value. Way too many deep pocket buyers trying to fill up vacant space in their cavernous garage. see also: more money than brains. There's also the issue of finding enough comps to get a feel for the market. Easy enough if you're looking at Vette or a baby Bird because there's always a ton of them. Maybe 1 or 2 70s Dodge trucks go through that tent every couple years.