What do you think about Adsense for Feeds? I have almost 700 subs, thinking of adding it. Personally I find it annoying when feeds use it, especially on top of the content. But I won't unsubscribe just based on that. I don't want to annoy my readers but it might be nice to monetize the feed other than the occasional affiliate link.
if you use it wisely at a minimum level, then it will not annoy your readers. you can test it with one ad block