Finding a complete old road bike for $100 in the Boston area takes some doing lately. Finding one for less than that is rare though they do pop up occasionally.
Here's a $100 Univega that was listed yesterday:
http://boston.craigslist.org/nos/bik/931585166.html
And a $40 Lambert that looks like it needs considerable work:
http://boston.craigslist.org/nwb/bik/931529581.html
Neal