Thanks for the comments, though my real question was not so much about how to be successful flipping bikes, rather more what
cb400bill was getting at: in my case I wasn't flipping anyway so the bike itself was essentially free, but replacing consumables (and being frugal about it) still put the minimal selling price above $100, no matter how crappy the original bike was. Even a better quality bike (I got a free Raleigh Record once and refurb'd it at my cost for a friend to use) would still need at least $100 in parts (using prices around here) but wouldn't sell for much more in good shape....Bill's numbers indicate a flipped bike that sells for less than $100-$150 is not going to happen, and doing the math more likely would have to sell for over $200. Around here you can still get plenty of decent bikes for that kind of money if you are looking for fairly low end. And
iab is right on the money: I put roughly 5 hours of time into the subject bike (mostly dealing with super low end V-brakes and getting them to work reasonably well - who would have thought two pieces of metal that *look* similar to decent v-brakes could be so awful?); I had to replace a couple of spokes which in turn required the right tools and a lot of ooomph getting the freewheel loose.....then truing the wheels, and so on.....
I had fun and every time you do something mechanical you improve your skills and learn something - so I am not grumbling. But when I see bikes that are being flipped I rarely see them at the price range that would cover basic consumables let alone labour - I can only assume that few of them get proper attention before the sale!
Edit: and just to be clear - I wouldn't normally have touched that bike - but it was a favour for a friend and I did make it clear that the bike was not a quality unit!