I decided to give blesta a try. I like it, and have flattened it's UI a bit. It was about 40 minutes of work (took me forever to get the buttons to work) to get the theme done.
http://billing.ssdpowered.com
user: 1234
pass: 123456
Of course, there's still a lot more that I could do, but I think this is pretty good for the amount of time it took.
Let me know what you think.