To subsidize or not to subsidize?
Many partner groups subsidize some allyship events. There are differing opinions on this. Some groups focus on principles: it's absurd that women would subsidize a group catering to men, and so they don't provide money. Other groups focus on impact, and decide that spending funds has the potential to influence more men to learn about inclusion so it's in alignment with their goals and an effective use of money.
What could subsidies accomplish?
Think about an "allyship lunch" event where everyone is invited to discuss D&I topics. If your goal is to get men to show up to think more about gender equity, using funds to buy food will almost definitely increase participation rates. It would be nice if men would be willing to show up without food, but many won't. Those who otherwise wouldn't have joined may also be those who are less receptive to D&I values – which could be a pro or a con, depending your goals.
You have a decision. There's not a right answer, but having a conversation about this topic (both "funding allyship groups" generally as well as particular events) amongst partner group leadership helps to ensure alignment of goals with funding.