A cheap mountain bike crank sounds good. I suppose this would work with the existing spindle?
Spindles are in different lengths to fit the bike bottom bracket.
Sorry, I've never worked on square taper cranks.
Shimano
Acera 42-32-22 triple, square taper. $34 !
Some smaller cranks for road bikes are available. Way more expensive, though.
Velo Orange
Grand Cru 30/46
White Industries VCB
cranksets and
chainrings for road bikes. inner ring choose 24 to 38, outer choose 38 to 52