I scored a DL-1 that way- just kept looking every day, and eventually got it. This was something like 8 or 10 years ago though. I would be willing to bet a higher price and faster sale today because of the Tweed element of the equation. In a way, it is good more people are appreciating the bikes and riding them. In a way it's bad because it makes life harder when you want parts/lower prices, at least in an environment where they're a hot ticket.

The one thing I will add is that many of the people getting them want road-ready versions and will pay a high price for them. It still seems to me that the guy who is willing to get one that needs work, and then can do the work himself, can make out well. I like them more than any of the new/more modern bikes I've ridden over the years.

I just flipped a lady's Humber made by Raleigh in '69.
I got it for $50, pristine but for a layer of dust and some odd cracks in the leather Brooks B72.
Sold it yesterday for $150. Usually I spend 3 or 4 hours cleaning them up and greasing everything. This one had a bent axle in the rear hub so I spent way more time. That's ok, it was a really good learning experience. Usually I ask more like $175 for one with a leather saddle and $125 without but this was suspicious so I split the difference. I was honest with the guy. That seat might brake tomorrow or it might last a lifetime. He understood and took it, even though I offered him a discount if he wanted to leave it.
He drove up from NYC in a rented Zip Car. I'm 45 minutes north of there. If I were in the city proper the price would be much higher but it's not worth the bridge tolls and time to try to get that extra dime. Some day I'll make a connection in the city and do more business there.
Last year a city flipper came out and bought 4 bikes. I should have saved his number, it was later that I figured that out.

Check this one out:

http://nmi.craigslist.org/bik/3098015184.html

Depends on condition and state of tune.

A basket case that is 90% complete can be found on Craigslist for $20-30 in a step-through and a little more than that for a diamond-frame. This depends on the size of the local market and availability. Sometimes you can find them in the junk for free.

If you want something that someone put a lot of time into cleaning up and doing a heavy tune-up into then add the price of that to the mix -most bike shops charge over $150 for this kind of work, more if there was a lot of parts that needed to be replaced and you want nicer high-end tires/brake pads (Kool Stops.)

Then if you are in an area where these bikes are becoming fad/hipster status symbols then the sky is the limit depending on condition.