221 featherweight would be a good choice. but way expensive
301 is aluminum bodied adn very nice
99 is a 3/4 machine and a small number of them were made of aluminum
Those are all Singers.
Post war Japanese machines were nearly all cast iron.
Some Domestics/Whites were made of magnesium but they don't have much of a following.[ATTACH=CONFIG]614401[/ATTACH]