"Hard up" is an idiomatic expression that means to be in a difficult financial situation. However, there are several synonyms that can be used in place of this expression. The first one is "broke," which is a well-known term for someone who has no money. Another synonym is "strapped for cash," which indicates a temporary lack of money. "In dire straits" and "penniless" are also good alternatives. Additionally, "down on one's luck," "financially challenged," and "impecunious" can be used to describe a person who is struggling financially. Finally, "tightfisted" refers to someone who is unwilling to spend money, which can also lead to financial hardship.