I've looked into using phplist to send a message to all of our registered users, but we are on dreamhost and they only allow, depending on how nicely you ask, about 500 to 700 emails an hour to go out. With almost 20k members it would take all day to send out a newsletter. Constant Contact has always looked like an attractive option with their metrics and I think if you can find a sponsor for your newsletter then you could easily offset the cost.
