On Chol HaMoed, one is not allowed to do melocho, even without excessive tircha or skill, if it's not l'tzorech hamo'ed (a need of the holiday) nor a davar ha'aved (financial loss).
How do we determine what is considered a davar ha'aved? Is there a shiur?
For example, if a sale occurs irregularly (e.g. twice a year) and presumably one would end up having to pay more money for the items or forgo its purchase entirely if he/she were to skip the sale, should that be considered a davar ha'aved?
Say we're not referring to a marketing "sale" of e.g. a department store but, e.g., a consignment sale of used items, where the price differences are actually significant from what one could find elsewhere, is there any reason to not allow shopping at the sale on Chol Hamoed for items that won't be used on the Mo'ed?