Apr'2014: But if you start with just JIRA and Confluence, their On Demand offering starts at $10/mo for up to 10 users. Jira Agile and BitBucket are "add-ons" which add $10/mo (each?). (Software Forge)
If you're willing to host it yourself, it's much cheaper. If you want to customize it, it's in Java.
2011: We started with two co-founders, and grew to 300 staff (no salespeople) in 6 countries. We sold about 60 million dollars worth of software last year... People don't mind paying for software, as long as they pay the same as everyone else. But with Enterprise software you’re not really sure what you are doing. So we came along, and our model we charge sort of under ten thousand dollars, you can download and use it. We don’t have any professional services, and so it’s quite different. These days it’s often known by a different name, Freemium, seems to be more and more common and more and more businesses seem to be following it.