Airplanes have been around over 100 years...what do you know about what's on sale today and what features/benefits you need, what is a good price, etc?
How about motorcycles? (100+ years) AR rifles? (50+ years), 1911 pistols (100+ years)? Teflon cookware?
Just because it's been around a long time and there is a 'consumer knowledge base' doesn't mean the consumer has a clue about it when it's time for them to buy it.
When I'm about to purchase something, it's not too difficult to Google "What does XXX cost?" and get at least a rough idea of what a product or service MIGHT cost.
I have a working knowledge of what a non-custom motorcycle would cost (been thinking about a HD Dyna for years), know what the costs for AR and 1911s are, and could take a pretty good swing at cookware .. airplanes not so much.
I think the point is one could easily get a base number to put into a budget that they could hit without too much effort. Whether that number holds up would depend on what choices the potential client made, but if they put down $600 for a DJ, I'm sure they could find a decent one .. maybe not you and maybe without some bells&whistles they might have wanted, but then they can decide if that would be worth it.
No different than car shopping. I'm searching for a replacement to my Pilot. I've looked at the websites, checked TrueCar .. I can walk into a dealer and know within $1K what I might be able to get a vehicle for .. and also know what I could get for a trade-in.