We have a client that uses Emma to promote their three annual conferences. This client’s database contains about 60,000 names and Emma handles it with ease. What I found great is that Emma is easy to use, has amazing design features and a ton of really great features like audience segmenting, drip abilities, and campaign automation.
Cost wise, they are not the most expensive or the least expensive but they do offer three tiers. Each tier include starts at lists up to 2500 and you go up in price with features and number of email addresses.
They do offer pricing for non-profits… be on the lookout for that.