As an economics/statistics/graph nerd I find this pretty fascinating. Excellent work!
I'm not surprised at the results...whenever I look at the TB Classifieds I find myself saying, "wow, I wish I could afford that," a lot more than I find myself saying, "I could realistically buy that," (granted, being a college student with little disposable income makes me a fairly bad sample). If I had the money I wouldn't hesitate to buy an expensive/exotic bass on TB as opposed to eBay or Craigslist; the sellers (and buyers) here are more knowledgeable and (from what I've seen) take better care of their gear than the Average Joe on eBay or CL does.
The reason the TB Classifieds are flooded with expensive basses is because we're a knowledgeable group of hobbyists/professionals that
own (and can afford) expensive basses. We're also not stupid...the demand for a Fodera/Zon/Vintage Fender/USA Lakland/Ritter is a lot higher on TB than it would be on eBay/CL, because we have an extensive amount of knowledge about these models. As said earlier in the thread, the Average Joe is bound to think that a USA Fender is
the Holy Grail of basses, mostly because it's "top shelf" at many GC locations. Plus, the goal of CL is about selling something you no longer need/use ("I bought this MIM Fender to pick up chicks but it didn't work...") to someone who wants a cheap item they don't know if they need/use ("Maybe if I buy this MIM Fender I'll pick up chicks"). CL to me is a lot more casual, hence the lower prices. Plus it's local, so you don't have to pay $80 to ship a $250 bass to your buyer, resulting in more profit.
And, because I was curious, I calculated the median price of all the basses on TB's first page in the classifieds...
$2285 by my calculations

(although I do admit to accidentally clearing my calculator of the final result, so that number is from memory

). The outliers at the time were an $8000 Fodera and a $300 (Upgraded) Squier...interesting stuff.