The price on these bikes varies wildly due to the whole supply and demand of it. They're not a very common bike where I live, so you rarely find them for sale locally. Prices vary from 800-5000 dollars for basically the same bike but different years and condition.
There's not much logic in the pricing of any one bike. My wife's Vespa is a 'ripoff' compared to a 150cc Chinese scooter, but if you're into nuance and appreciate quality you might be willing to pay for a steel bodied scooter that some guy in Italy painted professionally by hand
The TW has value in being a swiss army knife of a bike. It can go nearly anywhere (steet legally,) easy to ride, gets good gas mileage. The only one area it really lacks is in top speed if you ask me. People are willing to pay more money for stuff that is easy to ride. This is why Honda Rebel 250s will always cost more than their blue book value for old ones from the 80s. Blue book value is useless with used motorcycles. The best way to get a cheap, used motorcycle is to wait around forever. I'm not that sort of person. I just say to myself, "what's this thing worth to me?" I don't even consider what it might be worth to someone standing next to me. I just come up with a figure and shoot the number to the seller. Some days I come home with a new-to-me motorcycle and most days I don't.
Some of it's just cultural... I think Kawasaki KLR650 bikes and Suzuki Savage 650 bikes are both undervalued with horrible depreciation in my local economy. I can pick up a KLR650 cheaper than I can a TW200 here. But they sit high and weigh a lot, so they don't meet my personal needs. Thus I have my TW