Please help me BB users. my sister is getting married in oct and I want to give her a cash present as she has hinted to other family members that they would appreciate a cash gift because they are building their new home. I was wondering how much should i give?

I want to give them a nice present and I'm stressing it won't be enough. It's been 10 years plus since my older sister got married and I don't want to ask her how much she is giving. What is the average gift from a sibling?