Facebook-like chat plugin with a one-time fee?

I was wondering if anyone can reccomend a plugin that will tie into my WordPress installations for chat(like facebook chat). I also need the plugin to be a one-time fee.

Right now we are using Envolve. Luckily we were one of the first customers of Envolve so we locked in a pretty good price for our first website. However, now they want us to pay much more ($100/month) to increase our participant limit on our other sites which is just not feasible for us(we don’t sell anything, we provide free chat support and rely on advertising for income).

Can anyone recommend a good chat plugin that is like Facebook chat that will tie into our WordPress user database AND is only a one-time fee?

Thanks in advance!