Customer maintenance system development - PHP/MySQL expert needed

I am looking for an experienced PHP developer to work on additional features for a customer web application. It was developed from the ground-up about 5 years ago and needs extended. The application is similar to a online ticket system, but is focused for a specific market and has extensive administrator features built-in (time tracking, reports, etc).

This will be an hourly job - the amount of time required is undefined.

Some of the work will include:
- Phone conversations to get up to speed on the current web application, its functionality, features, etc.
- Getting up to speed on the current application's software structure, database structure, etc.
- Modifying the PHP code per the new spec to add additional features
- Modifying the database per the new spec
- Integrating the application with subscription-based payment gateway such as Authorize.net to handle new subscriptions, modifications to subscriptions, canceling subscriptions, etc. all seamlessly integrated into the application

Please quote the hourly rate assuming it will be a decent amount of hours, not just 5-10. Also, please reference examples of your work. Priority will be given to members with good reviews.

There will also be more opportunities for follow-up hourly work after this is completed, so the more competitive your hourly rate is, the better.

Thank you!