Revision pricing question

I have a client who I made a fundraising campaign booklet for a few months ago. Every few weeks they ask me to make a few small changes to it to put in names of people who donated money. I was charging them a set price for each time they asked me to make changes, which is higher than I would normally charge for a revision because its a much more annoying and tedious job.
They recently asked me if we could figure something out because they don’t like the price for each change every few weeks (which will continue for a while), which I understand because it is a bit high for a few small changes.
I’m not sure what to do because it’s really not worth my time to make the changes for less because of how annoying it is. Also I can’t tell them that they can find someone else because the job is making very tedious changes to my Illustrator and InDesign files.

Does anyone have any ideas what I can do? Should I offer to give them yearly rate? Should I offer to make a new file that is easier to make changes to and charge them for it and then charge a much much lower price for each change?

What about a “retainer” pricing. Which would be a set amount each month for you to give them X amount of hours of work or revisions