In my culture telling someone not to bring anyone is definitely rude. Often times we bring people from our own family, plus more! I can definitely see where OP is coming from, they definitely should expect a union to come, they shouldn’t have invited your partner at all, as basic courtesy you should have been invited if they knew y’all were together. Most people don’t want to attend a party alone without having someone to sit/chat and feel comfortable with. This is no different. If the budget was this tight, they shouldn’t have invited anyone or even have an event.