Gmail Chat Clone Script

I want somebody to develop a chat script for me which must be exactly in looks and working like Gmail Chat. do it in PHP or CGI, whichever is best to make it work. But the most important thing is, it must work with my existing Email Script. Which means, Whenever A User Signs up for an email from my email script, he will automatically get the Account at chat script. When User Logs in the email script, He must be able to access chat, see online users, chat privately, just all things like Gmail chat. The email script is made in CGI and uses MySql. You can use the existing database tables and settings from email script for chat script. My Budget is: $100