Essentially $100 to $120 per year. No thanks.

I still have and use my copy of Billings 3.7.8, and it works fine under Yosemite. I had considered updating, and I would have happily paid a fair price for this app, but not at 100 to 120 bucks PER YEAR. Forget it.

JTdesign about Billings Pro: Time & Invoice