on a shoestring

With very limited financial means, as in The newlyweds were living on a shoestring. The precise allusion in this term is unclear. One fanciful theory is that debtors in British prisons would lower a shoe by its laces from a window so as to collect funds from visitors or passers-by. A more likely theory is that it alludes to the slender shape of a shoelace, likening it to slender resources. [Late 1800s]