For me, cheapest and worst are not quite the same bike. They are both 1973 Raleighs - Cheapest would be the root beer colored Super Course that I picked up for $50. The stand-over height is just a little too high for me and the slack angles give the steering a "flop over" characteristic I don't care for. I'm using it as a repository for all the weird parts that have appeared on Super Courses over the years - Huret Luxe derailleurs, Capella lugs, Nervar Sport crankset, those long Huret shift levers, etc.... You can see the difference in the head tube angle between the '73 and '74 Super Courses in this photo.
The worst quality bike is this 1973 Gran Sport. I don't know how many pints the guy who brazed this had at lunch but several of the shorelines visible in this photo are recreated with touch-up paint. The front wheel has to be centered in the fork before closing the quick-release. However, this is one of the nicest-riding bikes I have ever had. I use it more than any other now. It's similar to a Super Course but a little lighter on it's feet (perhaps due to the double-butted frame tubes?) and since it is plain looking and I've only got $150 invested I don't feel bad about locking it up in front of the hardware store. It's a fun bike!