Pay per use is a difficult one, I think once you start complecting the pricing model like that people don't know where they stand. Personally I prefer simple.
I think your right the initial entry is a bit steep. The thing that scared the crap out of us with mailchimp was that there was no end in sight for price increases. If they had a max of $500 then we may have stayed on mailchimp. I guess our thought process was if you start with us you'll never leave because our prices will top out. But yes I think we'll introduce $5 for the first 1000 to get you going something like that maybe?
Yeah we did pay for http://sendy.co and admittedly spent way too much time looking at those shiny graphs.
Part of the problem we had with sendy was just general stability with the amount we where sending. All of sudden you need to support a mysql and php db. It was just another thing to worry about. So we thought if we have to worry about it lets write it ourselves.
I run www.markdownmail.io it's very simple with very limited features, emails are composed in markdown and templated with mustache. Everything is sent using your ses account which allows us to keep prices very low.