I'll roll out the standard reply here. There are plenty of other bikes that would fit the bill too - including some Schwinns (but you can go nuts trying to keep track of which of the "lightweights" really are).

Peugeot U-08 - plentiful, light, inexpensive, but blessed with parts manufactured to French "standards" up until about 1979. For 1980 (about) and later models, this is ceases to be an issue.

Raleigh Grand Prix - plentiful, inexpensive, larger pool of interchangeable parts, a bit heavier than the U-08, comes close after changing out the crankset and ditching steel wheels.