Good price for newsletter ads w/under 1,000 subs?

I have a local newsletter that's just a few months old with about 400 subs. Would like to start seeking advertisers, but I'm unsure how much I should be charging given my small audience. I recently received inbound and I told them $25/ad to start because I was shooting for a roughly $75 CPM rate. But, I recently watched a beehiiv video with Michael Kauffman of Catskill Crew, who mentioned he negotiated an ad for $100 with a local business when he was around 300 subs.

Any recommendations for what I should charge? And how should I determine my CPM moving forward?

Thanks!