This is your ex-partner's second marriage (if I understand your question)? I guess it depends how well you still know/like them...... we've given between £25 and £50 depending on the closeness of the relationship. Wwe were given similar amounts for our own wedding 5 years back if people didnt' want to give vouchers. If people asked what we wanted, we suggested help towards the cost of the wedding and people paid for specific items - registrar, help with bar costs, etc., which was nice.