@Olefoo you can get PostGIS on Heroku via SpacialDB. SpacialDB is cloud hosted PostGIS and a convenient RESTful API. We have a heroku addon too currently in private beta. Check out our devcenter here: http://devcenter.spacialdb.com/ and let us know if you would like a beta invite.
As of today, we only charge for the time you use. I don't imagine we'd ever need to change that, but never is a long time.
That is interesting, there are times when I want to use PG as an ETL tool and take a midsized ( < 2tb data ) set and load it up and slice and dice it and produce some output for other programs and then have it go away. So, I'll keep you guys in mind.
I am curious as to whether you do pro-rated pricing?